Method for producing aldehyde from CO2

ABSTRACT

The invention provides recombinant microorganisms capable of producing isobutyraldehyde using CO 2  as a carbon source. The invention further provides methods of preparing and using such microorganisms to produce isobutyraldehyde.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/US2009/068863, filed Dec. 18, 2009, which claims priority to U.S. Provisional Application No. 61/139,593, filed Dec. 20, 2008, and U.S. Provisional Application No. 61/219,322, filed Jun. 22, 2009, the disclosures of all of which are incorporated herein by reference in their entirety.

STATEMENT OF GOVERNMENT LICENSE RIGHTS

This invention was made with Government support under Grant No. DE-FC03-02ER63421 awarded by the United States Department of Energy. The Government has certain rights in this invention.

STATEMENT REGARDING SEQUENCE LISTING

The sequence listing associated with this application is provided in text format in lieu of a paper copy and is hereby incorporated by reference into the specification. The name of the text file containing the sequence listing is 37267_SEQ.txt. The text file is 289 KB; was created on Jun. 20, 2011; and is being submitted via EFS-Web with the filing of the specification.

BACKGROUND

According to the US Energy Information Administration (EIA, 2007), world energy-related CO₂ emissions in 2004 were 26,922 million metric tons and increased 26.7% from 1990. As a result, atmospheric levels of CO₂ have increased by about 25% over the past 150 years. Thus, it has become increasingly important to develop new technologies to reduce CO₂ emissions.

The world is also facing costly gas and oil and limited reserves of these precious resources. Biofuels have been recognized as an alternative energy source. While efforts have been made to improve various production, further developments are needed.

SUMMARY

The disclosure describes the construction of a novel metabolic system for conversion of CO₂ to various higher alcohols using photosynthetic microorganism such as, for example, cyanobacteria (Synechococcus elongatus PCC7942). There is currently no known method for production of higher alcohols from CO₂.

The disclosure describes the production of biofuels using metabolically engineered organisms that can utilize CO₂ as a starting material. An exemplary pathway is shown in FIG. 1A. This system can be used in any number of photosynthetic microorganisms. For example, one such organism is obtained from cyanobacteria. Large scale photobiorection can be performed on such bacteria. Using techniques described herein, isobutanol production from flask-fermentation using engineered strains of the disclosure were achieved.

The disclosure provides a recombinant photosynthetic organism comprising a pathway that converts CO₂ to metabolic intermediates that can be used in biofuel production. In one embodiment, a pathway starts from CO₂, which produces carbohydrate and various 2-keto acids via the Calvin Cycle, photosynthesis and amino acid pathways. The keto acid is converted to corresponding alcohols using promiscuous 2-keto-acid decarboxylase and alcohol dehydrogenase (ADH). The 2-keto-acid decarboxylase activity can be provided by one of the following genes: PDC6 from Saccharomyces cerevisiae, kind from Lactococcus lactis, and THI3 Saccharomyces cerevisiae (α-ketoisocaproate decarboxylase) and pdc Clostridium acetobutylicum. The alcohol dehydrogenase activity can be provided by ADH2 from Saccharomyces cerevisiae.

Thus, the disclosure provides metabolically-modified photosynthetic microorganisms that use CO₂ as a sole carbon source and include recombinant biochemical pathways useful for producing biofuels such as isobutanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 2-phenylethanol, 1-propanol, or 1-butanol via conversion of a suitable substrate by a metabolically engineered microorganism. Also provided are methods of producing biofuels using microorganisms described herein.

In one embodiment, a recombinant photosynthetic microorganism that produces an alcohol is provided. The alcohol can be 1-propanol, isobutanol, 1-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol or 2-phenylethanol. In general, the alcohol may be produced fermentatively or non-fermentatively (i.e., with or without the presence of oxygen) from a metabolite comprising 2-keto acid. In some embodiments, the 2-keto acid includes 2-ketobutyrate, 2-ketoisovalerate, 2-ketovalerate, 2-keto-3-methylvalerate, 2-keto-4-methyl-pentanoate, or phenylpyruvate. In other embodiments, the recombinant microorganism includes elevated expression or activity of a 2-keto-acid decarboxylase and an alcohol dehydrogenase, as compared to a parental microorganism. The 2-keto-acid decarboxylase may be Pdc6 from Saccharomyces cerevisiae, Aro10 from Saccharomyces cerevisiae, Thi3 from Saccharomyces cerevisiae, Kivd from Lactococcus lactis, or Pdc from Clostridium acetobutylicum, or homologs thereof. The 2-keto-acid decarboxylase can be encoded by a nucleic acid sequence derived from a gene selected from PDC6 from S. cerevisiae, ARO10 from S. cerevisiae, THI3 from S. cerevisiae, kivd from L. lactis, or pdc from C. acetobutylicum, or homologs thereof (See, e.g., SEQ ID NOs: 18-27). In some embodiments, the alcohol dehydrogenase may be Adh2 from S. cerevisiae, or homologs thereof (see, e.g., SEQ ID NO:28-29), encoded by a nucleic acid sequence derived from the ADH2 gene from S. cerevisiae. In another embodiment, a recombinant photoautotroph microorganism that produces isobutanol is provided. The microorganism includes elevated expression or activity of acetohydroxy acid synthase, acetohydroxy acid isomeroreductase, dihydroxy-acid dehydratase, 2-keto-acid decarboxylase, and alcohol dehydrogenase, as compared to a parental microorganism. As described herein the microorganism is derived from a parental organism that utilizes CO₂ as a sole carbon source (i.e., a photoautotroph).

The amino acid pathways can be amplified by either overexpression of targeted enzymes and/or by mutagenesis followed by amino acid analog selection. The step from keto acid to alcohols is achieved by expression of the corresponding proteins in the organism. This process can be achieved either in one organism or multiple organisms. In the latter case, for example, one organism produces keto acids from CO₂ and excretes the products to the medium, which are then converted to alcohols by the second organism.

Accordingly, the disclosure also provides a mixed culture comprising a photoautotroph microorganism and a recombinant photoheterotroph microorganism comprising a modified pathway for the production of a biofuel.

In some embodiments, the photoautotroph microorganism or a microorganism cultured with a photoautotroph can include elevated expression of acetolactate synthase, acetohydroxy acid isomeroreductase, dihydroxy-acid dehydratase, 2-keto-acid decarboxylase, and alchol dehydrogenase. In some embodiments, the recombinant microorganism further includes an elevated level of pyruvate as compared to a parental microorganism. The recombinant microorganism may further include the deletion or inhibition of expression of an adh, ldh, frd, fnr, pflB, or pta gene, or any combination thereof. In particular, the recombinant microorganism can include a deletion of adh, ldh, frd alone or in combination with fnr, fnr and pta, or pta and pflB. In one embodiment, the acetohydroxy acid synthase may be encoded by a polynucleotide derived from the ilvIH operon, ilvBN operon, ilvGM in E. coli, or the alsS gene from Bacillus subtilis, or homologs thereof. The ilvI gene of the ilvIH operon encodes an acetohydroxyacid synthase large subunit polypeptide and the ilvH gene of the ilvIH operon encodes an acetohydroxyacid synthase small subunit polypeptide. In another embodiment, the acetohydroxy acid isomeroreductase may be encoded by a polynucleotide derived from an ilvC gene in E. coli, or homologs thereof. In another embodiment, the dihydroxy-acid dehydratase may be encoded by a polynucleotide derived from an ilvD gene, or homologs thereof. In yet another aspect, the 2-keto-acid decarboxylase may be encoded by a nucleic acid sequence derived from a kivd gene from Lactococcus lactis or homologs thereof, or an ARO10 gene from S. cerevisiae, or homologs thereof. In a further embodiment, the alcohol dehydrogenase may be encoded by a polynucleotide derived from an ADH2 gene from S. cerevisiae, or homologs thereof.

In general the ilvIH operon of Escherichia coli encodes acetohydroxy acid synthase, the first enzyme in the isoleucine, valine and leucine biosynthetic pathway. The acetohydroxy acid synthase III isozyme, which catalyzes the first common step in the biosynthesis of isoleucine, leucine, and valine in Escherichia coli K-12, is composed of two subunits, the ilvI (acetohydroxyacid synthase III large subunit) and ilvH (acetohydroxyacid synthase small subunit) gene products. The ilvC gene of Escherichia coli encodes acetohydroxy acid isomeroreductase, the second enzyme in the parallel isoleucine-valine biosynthetic pathway. The ilvD gene of Escherichia coli encodes dihydroxy-acid dehydratase, the third enzyme in the isoleucine-valine biosynthetic pathway. In some embodiments the recombinant microorganism included an elevated expression of acetolactate synthase. The acetolactate synthase can be AlsS from Bacillus subtilis.

In one embodiment, a recombinant photoautotroph microorganism or combination culture comprising an photoautotroph and a recombinant microorganism that produces 1-butanol is provided. At least one microorganism includes elevated expression or activity of 2-isopropylmalate synthase, beta-isopropylmalate dehydrogenase, isopropylmalate isomerase, and threonine dehydratase, as compared to a parental microorganism. In another embodiment, the recombinant microorganism further includes increased levels of 2-ketovalerate, as compared to a parental microorganism. In another embodiment, the recombinant microorganism further includes decreased levels of 2-ketoisovalerate, 2-keto-3-methyl-valerate, or 2-keto-4-methyl-pentanoate, or any combination thereof, as compared to a parental microorganism. Accordingly, the microorganism may further include the deletion or inhibition of expression of an ilvD gene, as compared to a parental microorganism. In one embodiment, the 2-isopropylmalate synthase may be encoded by a polynucleotide derived from a leuA gene, or homologs thereof. In another aspect, the beta-isopropylmalate dehydrogenase may be encoded by a polynucleotide derived from a leuB gene, or homologs thereof. In yet another embodiment, the isopropylmalate isomerase may be encoded by a polynucleotide derived from a leuCD operon, or homologs thereof. In general the leuC gene of the leuCD operon encodes an isopropylmalate isomerase large subunit polypeptide and the leuD gene of the leuCD operon encodes an isopropylmalate isomerase small subunit polypeptide. In another embodiment, the threonine dehydratase may be encoded by a polynucleotide derived from an ilvA gene, or homologs thereof. In yet another embodiment, the threonine dehydratase may be encoded by a polynucleotide derived from a tdcB gene, or homologs thereof. In yet another embodiment, the recombinant microorganism may further include elevated expression or activity of pyruvate carboxylase, aspartate aminotransferase, homoserine dehydrogenase, aspartate-semialdehyde dehydrogenase, homoserine kinase, threonine synthase, L-serine dehydratase, or threonine dehydratase, or any combination thereof, as compared to a parental microorganism. In some embodiments, the pyruvate carboxylase, aspartate aminotransferase, homoserine dehydrogenase, aspartate-semialdehyde dehydrogenase, homoserine kinase, threonine synthase, L-serine dehydratase, and threonine dehydratase, are encoded by a polynucleotide derived from the ppc, pyc, aspC, thrA, asd, thrB, thrC, sdaAB, and tdcB genes, respectively, or homologs thereof.

In one embodiment, a recombinant photoautotroph microorganism or combination culture comprising an photoautotroph and a recombinant microorganism that produces 1-propanol is provided. The microorganism includes elevated expression or activity of alpha-isopropylmalate synthase, LeuB of Leptospira interrogans, isopropylmalate isomerase, and threonine dehydratase, as compared to a parental microorganism. In one embodiment, the alpha-isopropylmalate synthase may be encoded by a polynucleotide derived from a cimA gene, or homologs thereof. The cimA gene may be a Leptospira interrogans cimA gene or Methanocaldococcus jannaschii cimA gene. In another embodiment, the beta-isopropylmalate dehydrogenase may be encoded by a polynucleotide derived from a leuB gene, or homologs thereof. In another embodiment, the isopropylmalate isomerase may be encoded by a polynucleotide derived from a leuCD operon, or homologs thereof. In yet another embodiment, the recombinant microorganism may further include elevated expression or activity of phosphoenolpyruvate carboxylase, pyruvate carboxylase, aspartate aminotransferase, homoserine dehydrogenase, aspartate-semialdehyde dehydrogenase, homoserine kinase, threonine synthase, L-serine dehydratase, or threonine dehydratase, or any combination thereof, as compared to a parental microorganism. In some embodiments, the pyruvate carboxylase, aspartate aminotransferase, homoserine dehydrogenase, aspartate-semialdehyde dehydrogenase, homoserine kinase, threonine synthase, L-serine dehydratase, and threonine dehydratase, are encoded by a polynucleotide derived from the ppc, pyc, aspC, thrA, asd, thrB, thrC, sdaAB, and tdcB genes, respectively, or homologs thereof.

In another embodiment, a recombinant photoautotroph microorganism or combination culture comprising an photoautotroph and a recombinant microorganism that produces 2-methyl 1-butanol is provided. The microorganism includes elevated expression or activity of threonine dehydratase, acetohydroxy acid synthase, acetohydroxy acid isomeroreductase, dihydroxy-acid dehydratase, 2-keto-acid decarboxylase, and alcohol dehydrogenase, as compared to a parental microorganism, wherein the recombinant microorganism produces 2-methyl 1-butanol. In some embodiments, the threonine dehydratase may be encoded by a polynucleotide derived from an ilvA gene, or homologs thereof. In another embodiment, the threonine dehydratase may be encoded by a polynucleotide derived from a tdcB gene, or homologs thereof. In another embodiment, the recombinant microorganism further includes increased levels of 2-keto-3-methyl-valerate, as compared to a parental microorganism. In yet another embodiment, the 2-keto-acid decarboxylase may be encoded by a polynucleotide derived from a kivd gene, or homologs thereof, or a PDC6 gene, or homologs thereof, or THI3 gene, or homologs thereof.

In another embodiment, a recombinant photoautotroph microorganism or combination culture comprising a photoautotroph and a recombinant microorganism that produces 3-methyl 1-butanol is provided. The microorganism includes elevated expression or activity of acetohydroxy acid synthase or acetolactate synthase, acetohydroxy acid isomeroreductase, dihydroxy-acid dehydratase, 2-isopropylmalate synthase, isopropylmalate isomerase, beta-isopropylmalate dehydrogenase, 2-keto-acid decarboxylase, and alcohol dehydrogenase, as compared to a parental microorganism. In some embodiments, the acetohydroxy acid synthase may be encoded by a polynucleotide derived from an ilvIH operon, or homologs thereof. In another embodiment, the acetolactate synthase may be encoded by a polynucleotide derived from an alsS gene, or homologs thereof. In another embodiment, the acetolactate synthase may be encoded by a polynucleotide derived from an ilvMG operon, or homologs thereof. In another embodiment, the recombinant microorganism further includes increased levels of 2-ketoisocaproate, as compared to a parental microorganism. In yet another embodiment, the acetolactate synthase may be encoded by a polynucleotide derived from an ilvNB operon, or homologs thereof.

In another embodiment, a recombinant photoautotroph microorganism or combination culture comprising an photoautotroph and a recombinant microorganism that produces phenylethanol is provided. The microorganism includes elevated expression or activity of chorismate mutase P/prephenate dehydratase, chorismate mutase T/prephenate dehydrogenase, 2-keto-acid decarboxylase and alcohol dehydrogenase, as compared to a parental microorganism. In one embodiment, the chorismate mutase P/prephenate dehydratase may be encoded by a polynucleotide derived from a pheA gene, or homologs thereof. In another embodiment, the chorismate mutase T/prephenate dehydrogenase may be encoded by polynucleotide derived from a tyrA gene, or homologs thereof. In yet another embodiment, the recombinant microorganism further includes increased levels of phenylpyruvate, as compared to a parental microorganism.

In one embodiment, a method of producing a recombinant photoautotroph microorganism or combination culture comprising an photoautotroph and a recombinant microorganism that converts a suitable substrate or metabolic intermediate to 1-butanol is provided. The method includes transforming a microorganism with one or more recombinant polynucleotides encoding polypeptides comprising 2-isopropylmalate synthase activity, beta-isopropylmalate dehydrogenase activity, isopropylmalate isomerase activity, and threonine dehydratase activity.

In another embodiment, a method of producing a recombinant photoautotroph microorganism or combination culture comprising an photoautotroph and a recombinant microorganism that converts a suitable substrate or metabolic intermediate to isobutanol, is provided. The method includes transforming a microorganism with one or more recombinant nucleic acid sequences encoding polypeptides comprising acetohydroxy acid synthase activity, acetohydroxy acid isomeroreductase activity, dihydroxy-acid dehydratase activity, 2-keto-acid decarboxylase activity, and alcohol dehydrogenase activity.

In another embodiment, a method of producing a recombinant photoautotroph microorganism or combination culture comprising a photoautotroph and a recombinant microorganism that converts a suitable substrate or metabolic intermediate to 1-propanol, is provided. The method includes transforming a microorganism with one or more recombinant nucleic acid sequences encoding polypeptides comprising alpha-isopropylmalate synthase activity, beta-isopropylmalate dehydrogenase activity, isopropylmalate isomerase activity, and threonine dehydratase activity.

In one embodiment, a method of producing a recombinant photoautotroph microorganism or combination culture comprising an photoautotroph and a recombinant microorganism that converts a suitable substrate or metabolic intermediate to 2-methyl 1-butanol, is provided. The method includes transforming a microorganism with one or more recombinant nucleic acid sequences encoding polypeptides comprising threonine dehydratase activity, acetohydroxy acid synthase activity, acetohydroxy acid isomeroreductase activity, dihydroxy-acid dehydratase activity, 2-keto-acid decarboxylase activity, and alcohol dehydrogenase activity.

In another embodiment, a method of producing a recombinant photoautotroph microorganism or combination culture comprising a photoautotroph and a recombinant microorganism that converts a suitable substrate or metabolic intermediate to 3-methyl 1-butanol, is provided. The method includes transforming a microorganism with one or more recombinant nucleic acid sequences encoding polypeptides comprising acetohydroxy acid synthase activity or acetolactate synthase activity, acetohydroxy acid isomeroreductase activity, dihydroxy-acid dehydratase activity, 2-isopropylmalate synthase activity, isopropylmalate isomerase activity, beta-isopropylmalate dehydrogenase activity, 2-keto-acid decarboxylase activity, and alcohol dehydrogenase activity.

In another embodiment, a method of producing a recombinant photoautotroph microorganism or combination culture comprising an photoautotroph and a recombinant microorganism that converts a suitable substrate or metabolic intermediate to phenylethanol, is provided. The method includes transforming a microorganism with one or more recombinant nucleic acid sequences encoding polypeptides comprising chorismate mutase P/prephenate dehydratase activity, chorismate mutase T/prephenate dehydrogenase activity, 2-keto-acid decarboxylase activity, and alcohol dehydrogenase activity.

In another embodiment, a method of producing an alcohol, is provided. The method includes providing a recombinant photoautotroph microorganism or a culture comprising an photoautotroph and a recombinant microorganism provided herein; culturing the microorganism(s) in the presence of a suitable substrate or metabolic intermediate and under conditions suitable for the conversion of the substrate to an alcohol; and detecting the production of the alcohol. In various aspects, the alcohol is selected from 1-propanol, isobutanol, 1-butanol, 2-methyl 1-butanol, 3-methyl 1-butanol, and 2-phenylethanol. In another aspect, the substrate or metabolic intermediate includes a 2-keto acid, such as 2-ketobutyrate, 2-ketoisovalerate, 2-ketovalerate, 2-keto 3-methylvalerate, 2-keto 4-methyl-pentanoate, or phenylpyruvate.

The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more embodiments of the disclosure and, together with the detailed description, serve to explain the principles and implementations of the invention.

FIG. 1A depicts an exemplary synthetic non-fermentative pathway using 2-keto acid metabolism for alcohol production.

FIG. 1B depicts an exemplary alcohol production pathway in genetically engineered E. coli. Red arrowheads represent the 2-keto acid degradation pathway. Blue enzyme names represent amino acid biosynthesis pathways. Double lines represent a side-reaction of amino acid biosynthesis pathways.

FIG. 1C shows an exemplary biosynthetic pathway in photoautotrophs for the production of isobutylaldehyde.

FIGS. 1D-1J show isobutyraldehyde production from cyanobacteria. (D,E) Schematic representation of recombination to integrate kivd (D) alsS, ilvC and ilvD (E) genes into the S. elongatus chromosome. (F) Specific activities of AlsS, INC and IlvD in cell extracts of SA578 (with integrated kivd only) and SA590 (with integrated kivd, alsS, ilvC and ilvD). Error indicates s.d. (G) Cumulative production of isobutyraldehyde production by SA590. (H) Daily production rate of isobutyraldehyde by SA590. (I) Isobutyraldehyde concentration in the production culture of SA590. (J) Time courses for the growth of SA590. Error bars indicate s.d. (n=3).

FIGS. 1K-1L show ADH comparison for isobutanol production. (K) Comparison of isobutanol and isobutyraldehyde production by each combination of overexpression of ADHs with or without KIV (10 g/L) supplementation. The cells (SA413, SA561, SA562) were grown in shake flasks at 30° C. with 1 mM IPTG for 24 hr. (L) Isobutanol production and time courses for the growth of SA561 (without alsS-ilvC-ilvD (squares)) and SA579 (with alsS-ilvC-ilvD (circles)).

FIGS. 1M-1O show isobutanol production and comparison of various cyanobacterial and algal productivities. (M) Isobutanol production from NaHCO₃ using SA579 (with integrated alsS, ilvCD, kivd and yqhD) in shake flasks without stripping. Only trace amounts (<10 mg/l) of isobutyraldehyde were detected, indicating the dehydrogenase activity of YqhD was sufficient for isobutanol production. (N) Time course for the growth of SA579. Error bars indicate s.d. (n=3). (O) Productivity comparison of various processes. Productivities (μg l⁻¹ h⁻¹) of isobutyraldehyde production (this work), isobutanol production, ethanol production from S. elongatus1, hydrogen production from (1) Anabaena variabilis PK84, (2) Anabaena variabilis AVM13, (3) Chlamydomonas reinhardtii31 (4) Oscillatoria sp. Miami BG7, and lipid production from Haematococcus pluvialis.

FIGS. 1P-1Q show S. elongatus tolerance to isobutyraldehyde and isobutanol. Effect of isobutyraldehyde (P) or isobutanol (Q) addition on growing cultures of S. elongatus as determined by optical density (OD730). At OD730 ˜1.0, isobutyraldehyde or isobutanol was added to the cultures at final concentration (mg/L) of: 0 (squares), 500 (circles), 750 (triangles), 1000 (diamonds) and 2500 (stars).

FIG. 2 depicts modified amino acid biosynthesis pathways for improved isobutanol and 1-butanol production. Panel A shows isobutanol production with or without the engineered ilvIHCD pathway. Left panel: isobutanol production; Right panel: isobutanol yield per g of glucose. Theoretical maximum yield of isobutanol is 0.41 g/g. Panel B shows 1-butanol production with or without the engineered ilvA-leuABCD pathway from glucose. Left panel: 1-butanol production; Right panel: 1-propanol production in the same strain. Panel C shows 1-butanol production with L-threonine addition. Left panel: 1-butanol production; Right panel: 1-propanol production from the same strain.

FIG. 3 depicts an exemplary pathway for the production of 2-keto-isovalerate from pyruvate.

FIG. 4 depicts an exemplary pathway for leucine biosynthesis.

FIG. 5 depicts an exemplary pathway for isoleucine biosynthesis.

FIG. 6 depicts an exemplary pathway for butanol biosynthesis including 2-ketobutyrate as a biosynthetic intermediate.

FIG. 7 depicts an exemplary pathway for butanol biosynthesis from pyruvate.

FIG. 8 depicts an exemplary pathway for butanol biosynthesis including threonine as a biosynthetic intermediate.

FIG. 9 depicts exemplary biosynthetic pathways for the production of isobutanol (e.g., 2-methylpropyl alcohol), 3-methyl 1-butanol, 1-butanol, ethanol, 2-methyl 1-butanol, and 1-propanol.

FIG. 10 depicts exemplary biosynthetic pathways for the production of phenylethanol, ethanol, 3-methyl 1-butanol, and isobutanol (e.g., 2-methylpropyl alcohol).

FIG. 11 depicts a nucleic acid sequence derived from a kivd gene encoding a polypeptide having 2-keto-acid decarboxylase activity.

FIG. 12 depicts a nucleic acid sequence derived from a PDC6 gene encoding a polypeptide having 2-keto-acid decarboxylase activity.

FIG. 13 depicts a nucleic acid sequence derived from a ARO10 gene encoding a polypeptide having 2-keto-acid decarboxylase activity.

FIG. 14 depicts a nucleic acid sequence derived from an THI3 gene encoding a polypeptide having 2-keto-acid decarboxylase activity.

FIG. 15 depicts a nucleic acid sequence derived from an pdc gene encoding a polypeptide having 2-keto-acid decarboxylase activity.

FIG. 16 depicts a nucleic acid sequence derived from a ADH2 gene encoding a polypeptide having alcohol dehydrogenase activity.

FIG. 17 depicts a nucleic acid sequence derived from an ilvI gene encoding a polypeptide having acetolactate synthase large subunit activity.

FIG. 18 depicts a nucleic acid sequence derived from an ilvH gene encoding a polypeptide having acetolactate synthase small subunit activity.

FIG. 19 depicts a nucleic acid sequence derived from a ilvC gene encoding a polypeptide having acetohydroxy acid isomeroreductase activity.

FIG. 20 depicts a nucleic acid sequence derived from a ilvD gene encoding a polypeptide having dihydroxy-acid dehydratase activity.

FIG. 21 depicts a nucleic acid sequence derived from a ilvA gene encoding a polypeptide having threonine dehydratase activity.

FIG. 22 depicts a nucleic acid sequence derived from a leuA gene encoding a polypeptide having 2-isopropylmalate synthase activity.

FIG. 23 depicts a nucleic acid sequence derived from a leuB gene encoding a polypeptide having beta-isopropylmalate dehydrogenase activity.

FIG. 24 depicts a nucleic acid sequence derived from a leuC gene encoding a polypeptide having isopropylmalate isomerase large subunit activity.

FIG. 25 depicts a nucleic acid sequence derived from a leuD gene encoding a polypeptide having isopropylmalate isomerase small subunit activity.

FIG. 26 depicts a nucleic acid sequence derived from a cimA gene encoding a polypeptide having alpha-isopropylmalate synthase activity.

FIG. 27 depicts a nucleic acid sequence derived from a ilvM gene encoding a polypeptide having acetolactate synthase large subunit activity.

FIG. 28 depicts a nucleic acid sequence derived from a ilvG gene encoding a polypeptide having acetolactate synthase small subunit activity.

FIG. 29 depicts a nucleic acid sequence derived from a ilvN gene encoding a polypeptide having acetolactate synthase large subunit activity.

FIG. 30 depicts a nucleic acid sequence derived from a ilvB gene encoding a polypeptide having acetolactate synthase small subunit activity.

FIG. 31 depicts a nucleic acid sequence derived from a adhE2 gene encoding a polypeptide having alcohol dehydrogenase activity.

FIG. 32 depicts a nucleic acid sequence derived from a Li-cimA gene encoding a polypeptide having alpha-isopropylmalate synthase activity.

FIG. 33 depicts a nucleic acid sequence derived from a Li-leuC gene encoding a polypeptide having isopropylmalate isomerase large subunit activity.

FIG. 34 depicts a nucleic acid sequence derived from a Li-leuD gene encoding a polypeptide having isopropylmalate isomerase small subunit activity.

FIG. 35 depicts a nucleic acid sequence derived from a Li-leuB gene encoding a polypeptide having beta-isopropylmalate dehydrogenase activity.

FIG. 36 depicts a nucleic acid sequence derived from a pheA gene encoding a polypeptide having chorismate mutase P/prephenate dehydratase activity.

FIG. 37 depicts a nucleic acid sequence derived from a TyrA gene encoding a polypeptide having chorismate mutase T/prephenate dehydratase activity.

FIG. 38 depicts a nucleic acid sequence derived from an alsS gene encoding a polypeptide having acetolactate synthase activity.

FIG. 39 depicts an exemplary isobutanol production pathway via pyruvate.

FIG. 40 depicts an exemplary isobutanol production pathway via L-threonine.

FIG. 40A depicts reactions 1-5 of an exemplary 1-butanol production pathway via pyruvate.

FIG. 40B depicts reactions 6-7 of an exemplary 1-butanol production pathway via pyruvate.

FIG. 41 depicts an exemplary 1-propanol production pathway via L-threonine.

FIG. 42 depicts an exemplary 1-propanol production pathway via pyruvate.

FIG. 43 depicts an exemplary 2-methyl-1-butanol production pathway via L-threonine.

FIG. 43A depicts reactions 1-8 of an exemplary 3-methyl-1-butanol production pathway via pyruvate.

FIG. 43B depicts reaction 9 of an exemplary 3-methyl-1-butanol production pathway via pyruvate.

FIG. 44 depicts an exemplary phenyl-ethanol production pathway via chorismate.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

As used herein and in the appended claims, the singular forms “a,” “and,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a microorganism” includes a plurality of such microorganisms and reference to “the polypeptide” includes reference to one or more polypeptides and equivalents thereof, and so forth.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although any methods and reagents similar or equivalent to those described herein can be used in the practice of the disclosed methods and compositions, the exemplary methods and materials are now described.

Also, the use of “or” means “and/or” unless stated otherwise. Similarly, “comprise,” “comprises,” “comprising” “include,” “includes,” and “including” are interchangeable and not intended to be limiting.

It is to be further understood that where descriptions of various embodiments use the term “comprising,” those skilled in the art would understand that in some specific instances, an embodiment can be alternatively described using language “consisting essentially of” or “consisting of.”

All publications mentioned herein are incorporated herein by reference in full for the purpose of describing and disclosing the methodologies, which are described in the publications, which might be used in connection with the description herein. The publications discussed above and throughout the text are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the inventors are not entitled to antedate such disclosure by virtue of prior disclosure.

The disclosure provides methods and compositions for the production of higher alcohols using a culture of microorganisms that utilizes CO₂ as a carbon source. Examples of such microorganisms that utilize CO₂ as a carbon source include photoautotrophs. In some embodiments, that methods and compositions comprise a co-culture of photoautotrophs and a photoheterotroph or a photoautotroph and a microorganism that cannot utilize CO₂ as a carbon source.

In various embodiments the metabolically engineered microorganisms or combination cultures provided herein include biochemical pathways for the production of high alcohols including isobutanol, 1-butanol, 1-propanol, 2-methyl-1-butanol, 3-methyl-1-butanol and 2-phenylethanol from a suitable substrate. In various embodiments a recombinant microorganism provided herein includes the elevated expression or expression of a heterologous polypeptide of at least one target enzyme as compared to a parental microorganism. The recombinant microorganism also produces at least one metabolite involved in a biosynthetic pathway for the production of isobutanol, 1-butanol, 1-propanol, 2-methyl-1-butanol, 3-methyl-1-butanol or 2-phenylethanol. In general, the microorganisms or combination culture provided herein include at least one recombinant metabolic pathway that includes a target enzyme. The pathway acts to modify a substrate or metabolic intermediate in the production of isobutanol, 1-butanol, 1-propanol, 2-methyl-1-butanol, 3-methyl-1-butanol or 2-phenylethanol. The target enzyme is encoded by, and expressed from, a nucleic acid sequence derived from a suitable biological source. In some embodiments the polynucleotide is a gene derived from a bacterial or yeast source.

As used herein, the term “metabolically engineered” or “metabolic engineering” involves rational pathway design and assembly of biosynthetic genes, genes associated with operons, and control elements of such nucleic acid sequences, for the production of a desired metabolite, such as a 2-keto acid or high alcohol, in a microorganism. “Metabolically engineered” can further include optimization of metabolic flux by regulation and optimization of transcription, translation, protein stability and protein functionality using genetic engineering and appropriate culture condition. The biosynthetic genes can be heterologous to the host (e.g., microorganism), either by virtue of being foreign to the host, or being modified by mutagenesis, recombination, and/or association with a heterologous expression control sequence in an endogenous host cell. Appropriate culture conditions are conditions of culture medium pH, ionic strength, nutritive content, etc.; temperature; oxygen/CO₂/nitrogen content; humidity; and other culture conditions that permit production of the compound by the host microorganism, i.e., by the metabolic action of the microorganism. Appropriate culture conditions are well known for microorganisms that can serve as host cells.

Accordingly, metabolically “engineered” or “modified” microorganisms are produced via the introduction of genetic material into a host or parental microorganism of choice thereby modifying or altering the cellular physiology and biochemistry of the microorganism. Through the introduction of genetic material the parental microorganism acquires new properties, e.g. the ability to produce a new, or greater quantities of, an intracellular metabolite. In an illustrative embodiment, the introduction of genetic material into a parental microorganism results in a new or modified ability to produce an alcohol such as 1-propanol, isobutanol, 1-butanol, 2-methyl 1-butanol, 3-methyl 1-butanol or 2-phenylethanol. The genetic material introduced into the parental microorganism contains gene(s), or parts of genes, coding for one or more of the enzymes involved in a biosynthetic pathway for the production of an alcohol and may also include additional elements for the expression and/or regulation of expression of these genes, e.g. promoter sequences.

Microorganisms provided herein are modified to produce metabolites in quantities not available in the parental microorganism. A “metabolite” refers to any substance produced by metabolism or a substance necessary for or taking part in a particular metabolic process. A metabolite can be an organic compound that is a starting material (e.g., glucose or pyruvate) in, an intermediate (e.g., 2-keto acid) in, or an end product (e.g., 1-propanol, isobutanol, 1-butanol, 2-methyl 1-butanol, 3-methyl 1-butanol or 2-phenylethanol) of metabolism. Metabolites can be used to construct more complex molecules, or they can be broken down into simpler ones. Intermediate metabolites may be synthesized from other metabolites, perhaps used to make more complex substances, or broken down into simpler compounds, often with the release of chemical energy. End products of metabolism are the final result of the breakdown of other metabolites.

FIG. 1A shows a general pathway for production of a biofuel in a recombinant microorganism or co-culture of the disclosure from CO₂ as a carbon source. Exemplary metabolites include glucose, pyruvate, 1-propanol, isobutanol, 1-butanol, 2-methyl 1-butanol, 3-methyl 1-butanol or 2-phenylethanol, and 2-keto acids. As depicted in FIG. 1B, exemplary 2-keto acids include 2-ketobutyrate, 2-ketoisovalerate, 2-ketovalerate, 2-keto 3-methylvalerate, 2-keto 4-methyl-pentanoate, and phenylpyruvate. The exemplary 2-keto acids shown in FIG. 1B may be used as metabolic intermediates in the production of 1-propanol, isobutanol, 1-butanol, 2-methyl 1-butanol, 3-methyl 1-butanol or 2-phenylethanol. For example, as shown in FIG. 1B a recombinant microorganism metabolically engineered to provide elevated expression of enzymes encoded by LeuABCD produces 2-ketovalerate from 2-ketobutyrate. The 2-ketovalerate metabolite may be used to produce 1-butanol by additional enzymes produced by the metabolically modified microorganism. Additionally, 1-propanol and 2-methyl 1-butanol can be produced from 2-ketobutyrate and 2-keto-3-methyl-valerate by a recombinant microorganism metabolically engineered to express or over-express enzymes encoded by ilvIHDC, KDC and ADH genes. Further, the metabolite 2-ketoisovalerate can be produced by a recombinant microorganism metabolically engineered to express or over-express enzymes encoded by ilvIHCD genes. This metabolite can then be used in the production of isobutanol or 3-methyl 1-butanol. The metabolites pyruvate and phenylpyruvate can be used to produce 2-phenylethanol by a recombinant microorganism metabolically engineered to express or over-express enzymes encoded by KDC and ADH. Additional metabolites and genes are shown in FIG. 1B.

The term “biosynthetic pathway”, also referred to as “metabolic pathway”, refers to a set of anabolic or catabolic biochemical reactions for converting (transmuting) one chemical species into another. Gene products belong to the same “metabolic pathway” if they, in parallel or in series, act on the same substrate, produce the same product, or act on or produce a metabolic intermediate (i.e., metabolite) between the same substrate and metabolite end product.

The term “substrate” or “suitable substrate” refers to any substance or compound that is converted or meant to be converted into another compound by the action of an enzyme. The term includes not only a single compound, but also combinations of compounds, such as solutions, mixtures and other materials which contain at least one substrate, or derivatives thereof. Further, the term “substrate” encompasses not only compounds that provide a carbon source suitable for use as a starting material, such as any biomass derived sugar, but also intermediate and end product metabolites used in a pathway associated with a metabolically engineered microorganism as described herein. A “biomass derived sugar” includes, but is not limited to, molecules such as glucose, mannose, xylose, and arabinose or sugars or intermediates produced by a photosynthetic microorganism. The term biomass derived sugar encompasses suitable carbon substrates ordinarily used by microorganisms, such as 6 carbon sugars, including but not limited to gulose, lactose, sorbose, fructose, idose, galactose and mannose all in either D or L form, or a combination of 6 carbon sugars, such as glucose and fructose, and/or 6 carbon sugar acids including, but not limited to, 2-keto-L-gulonic acid, idonic acid (IA), gluconic acid (GA), 6-phosphogluconate, 2-keto-D-gluconic acid (2 KDG), 5-keto-D-gluconic acid, 2-ketogluconatephosphate, 2,5-diketo-L-gulonic acid, 2,3-L-diketogulonic acid, dehydroascorbic acid, erythorbic acid (EA) and D-mannonic acid.

The term “alcohol” includes for example 1-propanol, isobutanol, 1-butanol, 2-methyl 1-butanol, 3-methyl 1-butanol or 2-phenylethanol. The term “1-butanol” generally refers to a straight chain isomer with the alcohol functional group at the terminal carbon. The straight chain isomer with the alcohol at an internal carbon is sec-butanol or 2-butanol. The branched isomer with the alcohol at a terminal carbon is isobutanol, and the branched isomer with the alcohol at the internal carbon is tert-butanol.

Recombinant microorganisms provided herein can express a plurality of target enzymes involved in pathways for the production of e.g., 1-propanol, isobutanol, 1-butanol, 2-methyl 1-butanol, 3-methyl 1-butanol or 2-phenylethanol, from using a suitable carbon substrate.

Accordingly, provided herein are recombinant microorganisms that produce isobutanol and in some embodiments may include the elevated expression of target enzymes such as acetohydroxy acid synthase (ilvIH operon), acetohydroxy acid isomeroreductase (ilvC), dihydroxy-acid dehydratase (ilvD), 2-keto-acid decarboxylase (PDC6, ARO10, THI3, kivd, or pdc), and alcohol dehydrogenase (ADH2). The microorganism may further include the deletion or inhibition of expression of an adh (e.g., an adhE), ldh (e.g., an ldhA), frd (e.g., an frdB, an frdC or an frdBC), fnr, pflB, or pta gene, or any combination thereof, to increase the availability of pyruvate. In some embodiments the recombinant microorganism may include the elevated expression of acetolactate synthase (alsS), acteohydroxy acid isomeroreductase (ilvC), dihydroxy-acid dehydratase (ilvD), 2-keto acid decarboxylase (PDC6, ARO10, TH13, kivd, or pdc), and alcohol dehydrogenase (ADH2). In one embodiment, the recombinant microorganism is an autophototroph or may be a non-photosynthetic organism recombinantly engineered to produce the alcohol that is cultured in combination with a autophototroph to fix CO₂.

Also provided are recombinant microorganisms that produce 1-butanol and may include the elevated expression of target enzymes such as 2-isopropylmalate synthase (leuA), beta-isopropylmalate dehydrogenase (leuB), isopropylmalate isomerase (leuCD operon), threonine dehydratase (ilvA). The microorganism may be a autophotroph microorganism or a non-photosynthetic or heterotrophic microorganism. The microorganism may further include decreased levels of 2-ketoisovalerate, 2-keto-3-methyl-valerate, or 2-keto-4-methyl-pentanoate, or any combination thereof, as compared to a parental microorganism. In addition, the microorganism may include the deletion or inhibition of expression of an ilvD gene, as compared to a parental microorganism. A recombinant microorganism that produces 1-butanol and may include further elevated expression or activity of pyruvate carboxylase, aspartate aminotransferase, homoserine dehydrogenase, aspartate-semialdehyde dehydrogenase, homoserine kinase, threonine synthase, L-serine dehydratase, and/or threonine dehydratase, encoded by a nucleic acid sequences derived from the ppc, pyc, aspC, thrA, asd, thrB, thrC, sdaAB, and tdcB genes, respectively.

Also provided are recombinant microorganisms that produce 1-propanol and may include the elevated expression of target enzymes such as alpha-isopropylmalate synthase (cimA), beta-isopropylmalate dehydrogenase (leuB), isopropylmalate isomerase (leuCD operon) and threonine dehydratase.

Also provided are recombinant microorganisms that produce 2-methyl 1-butanol and may include the elevated expression of target enzymes such as threonine dehydratase (ilvA or tdcB), acetohydroxy acid synthase (ilvIH operon), acetohydroxy acid isomeroreductase (ilvC), dihydroxy-acid dehydratase (ilvD), 2-keto-acid decarboxylase (PDC6, ARO10, THI3, kivd, and/or pdc, and alcohol dehydrogenase (ADH2).

Also provided are recombinant photoautotroph microorganism(s) or culture comprising a photoautotroph and a recombinant non-photosynthetic or photoheterotroph microorganism that produce 3-methyl 1-butanol and may include the elevated expression of target enzymes such as acetolactate synthase (alsS), acetohydroxy acid synthase (ilvIH), acetolactate synthase (ilvMG) or (ilvNB), acetohydroxy acid isomeroreductase (ilvC), dihydroxy-acid dehydratase (ilvD), 2-isopropylmalate synthase (leuA), isopropylmalate isomerase (leuCD operon), beta-isopropylmalate dehydrogenase (leuB), 2-keto-acid decarboxylase (kivd, PDC6, or THI3), and alcohol dehydrogenase (ADH2).

Also provided are recombinant photoautotroph microorganism(s) or culture comprising a photoautotroph and a recombinant non-photosynthetic or photoheterotroph microorganism that produce phenylethanol and may include the elevated expression of target enzymes such as chorismate mutase P/prephenate dehydratase (pheA), chorismate mutase T/prephenate dehydrogenase (tyrA), 2-keto-acid decarboxylase (kivd, PDC6, or THI3), and alcohol dehydrogenase (ADH2).

As previously noted the target enzymes described throughout this disclosure generally produce metabolites. For example, the enzymes 2-isopropylmalate synthase (leuA), beta-isopropylmalate dehydrogenase (leuB), and isopropylmalate isomerase (leuCD operon) may produce 2-ketovalerate from a substrate that includes 2-ketobutyrate. In addition, the target enzymes described throughout this disclosure are encoded by nucleic acid sequences. For example, threonine dehydratase can be encoded by a nucleic acid sequence derived from an ilvA gene. Acetohydroxy acid synthase can be encoded by a nucleic acid sequence derived from an ilvIH operon. Acetohydroxy acid isomeroreductase can be encoded by a nucleic acid sequence derived from an ilvC gene. Dihydroxy-acid dehydratase can be encoded by a nucleic acid sequence derived from an ilvD gene. 2-keto-acid decarboxylase can be encoded by a nucleic acid sequence derived from a PDC6, ARO10, THI3, kivd, and/or pdc gene. Alcohol dehydrogenase can be encoded by a nucleic acid sequence derived from an ADH2 gene. Additional enzymes and exemplary genes are described throughout this document. Homologs of the various polypeptides and nucleic acid sequences can be derived from any biologic source that provides a suitable nucleic acid sequence encoding a suitable enzyme.

It is understood that a range of microorganisms can be modified to include a recombinant metabolic pathway suitable for the production of e.g., 1-propanol, isobutanol, 1-butanol, 2-methyl 1-butanol, 3-methyl 1-butanol or 2-phenylethanol. It is also understood that various microorganisms can act as “sources” for genetic material encoding target enzymes suitable for use in a recombinant microorganism provided herein. The term “microorganism” includes prokaryotic and eukaryotic photosynthetic microbial species. The terms “microbial cells” and “microbes” are used interchangeably with the term microorganism.

“Bacteria”, or “eubacteria”, refers to a domain of prokaryotic organisms. Bacteria include at least 11 distinct groups as follows: (1) Gram-positive (gram+) bacteria, of which there are two major subdivisions: (1) high G+C group (Actinomycetes, Mycobacteria, Micrococcus, others) (2) low G+C group (Bacillus, Clostridia, Lactobacillus, Staphylococci, Streptococci, Mycoplasmas); (2) Proteobacteria, e.g., Purple photosynthetic+non-photosynthetic Gram-negative bacteria (includes most “common” Gram-negative bacteria); (3) Cyanobacteria, e.g., oxygenic phototrophs; (4) Spirochetes and related species; (5) Planctomyces; (6) Bacteroides, Flavobacteria; (7) Chlamydia; (8) Green sulfur bacteria; (9) Green non-sulfur bacteria (also anaerobic phototrophs); (10) Radioresistant micrococci and relatives; (11) Thermotoga and Thermosipho thermophiles.

“Gram-negative bacteria” include cocci, nonenteric rods, and enteric rods. The genera of Gram-negative bacteria include, for example, Neisseria, Spirillum, Pasteurella, Brucella, Yersinia, Francisella, Haemophilus, Bordetella, Escherichia, Salmonella, Shigella, Klebsiella, Proteus, Vibrio, Pseudomonas, Bacteroides, Acetobacter, Aerobacter, Agrobacterium, Azotobacter, Spirilla, Serratia, Vibrio, Rhizobium, Chlamydia, Rickettsia, Treponema, and Fusobacterium.

“Gram positive bacteria” include cocci, nonsporulating rods, and sporulating rods. The genera of gram positive bacteria include, for example, Actinomyces, Bacillus, Clostridium, Corynebacterium, Erysipelothrix, Lactobacillus, Listeria, Mycobacterium, Myxococcus, Nocardia, Staphylococcus, Streptococcus, and Streptomyces.

Photoautotrophic bacteria are typically Gram-negative rods which obtain their energy from sunlight through the processes of photosynthesis. In this process, sunlight energy is used in the synthesis of carbohydrates, which in recombinant photoautotrophs can be further used as intermediates in the synthesis of biofuels. In other embodiments, the photoautotrophs serve as a source of carbohydrates for use by non-photosynthetic microorganisms (e.g., recombinant E. coli) to produce biofuels by a metabolically engineered microorganism. Certain photoautotrophs called anoxygenic photoautotrophs grow only under anaerobic conditions and neither use water as a source of hydrogen nor produce oxygen from photosynthesis. Other photoautotrophic bacteria are oxygenic photoautotrophs. These bacteria are typically cyanobacteria. They use chlorophyll pigments and photosynthesis in photosynthetic processes resembling those in algae and complex plants. During the process, they use water as a source of hydrogen and produce oxygen as a product of photosynthesis.

Cyanobacteria include various types of bacterial rods and cocci, as well as certain filamentous forms. The cells contain thylakoids, which are cytoplasmic, platelike membranes containing chlorophyll. The organisms produce heterocysts, which are specialized cells believed to function in the fixation of nitrogen compounds.

The term “recombinant microorganism” and “recombinant host cell” are used interchangeably herein and refer to microorganisms that have been genetically modified to express or over-express endogenous nucleic acid sequences, or to express non-endogenous sequences, such as those included in a vector. The nucleic acid sequence generally encodes a target enzyme involved in a metabolic pathway for producing a desired metabolite as described above. Accordingly, recombinant microorganisms described herein have been genetically engineered to express or over-express target enzymes not previously expressed or over-expressed by a parental microorganism. It is understood that the terms “recombinant microorganism” and “recombinant host cell” refer not only to the particular recombinant microorganism but to the progeny or potential progeny of such a microorganism.

A “parental microorganism” refers to a cell used to generate a recombinant microorganism. The term “parental microorganism” describes a cell that occurs in nature, i.e. a “wild-type” cell that has not been genetically modified. The term “parental microorganism” also describes a cell that has been genetically modified but which does not express or over-express a target enzyme e.g., an enzyme involved in the biosynthetic pathway for the production of a desired metabolite such as 1-propanol, isobutanol, 1-butanol, 2-methyl 1-butanol, 3-methyl 1-butanol or 2-phenylethanol. For example, a wild-type microorganism can be genetically modified to express or over express a first target enzyme such as thiolase. This microorganism can act as a parental microorganism in the generation of a microorganism modified to express or over-express a second target enzyme e.g., hydroxybutyryl CoA dehydrogenase. In turn, the microorganism modified to express or over express e.g., thiolase and hydroxybutyryl CoA dehydrogenase can be modified to express or over express a third target enzyme e.g., crotonase. Accordingly, a parental microorganism functions as a reference cell for successive genetic modification events. Each modification event can be accomplished by introducing a nucleic acid molecule in to the reference cell. The introduction facilitates the expression or over-expression of a target enzyme. It is understood that the term “facilitates” encompasses the activation of endogenous nucleic acid sequences encoding a target enzyme through genetic modification of e.g., a promoter sequence in a parental microorganism. It is further understood that the term “facilitates” encompasses the introduction of exogenous nucleic acid sequences encoding a target enzyme in to a parental microorganism.

In another embodiment a method of producing a recombinant microorganism that converts a suitable carbon substrate to e.g., 1-propanol, isobutanol, 1-butanol, 2-methyl 1-butanol, 3-methyl 1-butanol or 2-phenylethanol is provided. The method includes transforming a microorganism with one or more recombinant nucleic acid sequences encoding polypeptides that include e.g., acetohydroxy acid synthase (ilvIH operon), acetohydroxy acid isomeroreductase (ilvC), dihydroxy-acid dehydratase (ilvD), 2-keto-acid decarboxylase (PDC6, ARO10, THI3, kivd, or pdc), 2-isopropylmalate synthase (leuA), beta-isopropylmalate dehydrogenase (leuB), isopropylmalate isomerase (leuCD operon), threonine dehydratase (ilvA), alpha-isopropylmalate synthase (cimA), beta-isopropylmalate dehydrogenase (leuB), isopropylmalate isomerase (leuCD operon), threonine dehydratase (ilvA), acetolactate synthase (ilvMG or ilvNB), acetohydroxy acid isomeroreductase (ilvC), dihydroxy-acid dehydratase (ilvD), beta-isopropylmalate dehydrogenase (leuB), chorismate mutase P/prephenate dehydratase (pheA), chorismate mutase T/prephenate dehydrogenase (tyrA), 2-keto-acid decarboxylase (kivd, PDC6, or THI3), and alcohol dehydrogenase activity. Nucleic acid sequences that encode enzymes useful for generating metabolites including homologs, variants, fragments, related fusion proteins, or functional equivalents thereof, are used in recombinant nucleic acid molecules that direct the expression of such polypeptides in appropriate host cells, such as bacterial or yeast cells. It is understood that the addition of sequences which do not alter the encoded activity of a nucleic acid molecule, such as the addition of a non-functional or non-coding sequence, is a conservative variation of the basic nucleic acid. The “activity” of an enzyme is a measure of its ability to catalyze a reaction resulting in a metabolite, i.e., to “function”, and may be expressed as the rate at which the metabolite of the reaction is produced. For example, enzyme activity can be represented as the amount of metabolite produced per unit of time or per unit of enzyme (e.g., concentration or weight), or in terms of affinity or dissociation constants.

A “protein” or “polypeptide”, which terms are used interchangeably herein, comprises one or more chains of chemical building blocks called amino acids that are linked together by chemical bonds called peptide bonds. An “enzyme” means any substance, composed wholly or largely of protein, that catalyzes or promotes, more or less specifically, one or more chemical or biochemical reactions. The term “enzyme” can also refer to a catalytic polynucleotide (e.g., RNA or DNA). A “native” or “wild-type” protein, enzyme, polynucleotide, gene, or cell, means a protein, enzyme, polynucleotide, gene, or cell that occurs in nature.

Accordingly, homologs of enzymes useful for generating metabolites (e.g., keto thiolase, acetyl-CoA acetyltransferase, hydroxybutyryl CoA dehydrogenase, crotonase, crotonyl-CoA reductase, butyryl-coA dehydrogenase, alcohol dehydrogenase (ADH)) are encompassed by the microorganisms and methods provided herein. The term “homologs” used with respect to an original enzyme or gene of a first family or species refers to distinct enzymes or genes of a second family or species which are determined by functional, structural or genomic analyses to be an enzyme or gene of the second family or species which corresponds to the original enzyme or gene of the first family or species. Most often, homologs will have functional, structural or genomic similarities. Techniques are known by which homologs of an enzyme or gene can readily be cloned using genetic probes and PCR. Identity of cloned sequences as homolog can be confirmed using functional assays and/or by genomic mapping of the genes.

A protein has “homology” or is “homologous” to a second protein if the nucleic acid sequence that encodes the protein has a similar sequence to the nucleic acid sequence that encodes the second protein. Alternatively, a protein has homology to a second protein if the two proteins have “similar” amino acid sequences. (Thus, the term “homologous proteins” is defined to mean that the two proteins have similar amino acid sequences).

As used herein, two proteins (or a region of the proteins) are substantially homologous when the amino acid sequences have at least about 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity. To determine the percent identity of two amino acid sequences, or of two nucleic acid sequences, the sequences are aligned for optimal comparison purposes (e.g., gaps can be introduced in one or both of a first and a second amino acid or nucleic acid sequence for optimal alignment and non-homologous sequences can be disregarded for comparison purposes). In one embodiment, the length of a reference sequence aligned for comparison purposes is at least 30%, typically at least 40%, more typically at least 50%, even more typically at least 60%, and even more typically at least 70%, 80%, 90%, 100% of the length of the reference sequence. The amino acid residues or nucleotides at corresponding amino acid positions or nucleotide positions are then compared. When a position in the first sequence is occupied by the same amino acid residue or nucleotide as the corresponding position in the second sequence, then the molecules are identical at that position (as used herein amino acid or nucleic acid “identity” is equivalent to amino acid or nucleic acid “homology”). The percent identity between the two sequences is a function of the number of identical positions shared by the sequences, taking into account the number of gaps, and the length of each gap, which need to be introduced for optimal alignment of the two sequences.

When “homologous” is used in reference to proteins or peptides, it is recognized that residue positions that are not identical often differ by conservative amino acid substitutions. A “conservative amino acid substitution” is one in which an amino acid residue is substituted by another amino acid residue having a side chain (R group) with similar chemical properties (e.g., charge or hydrophobicity). In general, a conservative amino acid substitution will not substantially change the functional properties of a protein. In cases where two or more amino acid sequences differ from each other by conservative substitutions, the percent sequence identity or degree of homology may be adjusted upwards to correct for the conservative nature of the substitution. Means for making this adjustment are well known to those of skill in the art (see, e.g., Pearson et al., 1994, hereby incorporated herein by reference).

The following six groups each contain amino acids that are conservative substitutions for one another: 1) Serine (S), Threonine (T); 2) Aspartic Acid (D), Glutamic Acid (E); 3) Asparagine (N), Glutamine (Q); 4) Arginine (R), Lysine (K); 5) Isoleucine (I), Leucine (L), Methionine (M), Alanine (A), Valine (V), and 6) Phenylalanine (F), Tyrosine (Y), Tryptophan (W).

Sequence homology for polypeptides, which is also referred to as percent sequence identity, is typically measured using sequence analysis software. See, e.g., the Sequence Analysis Software Package of the Genetics Computer Group (GCG), University of Wisconsin Biotechnology Center, 910 University Avenue, Madison, Wis. 53705. Protein analysis software matches similar sequences using measure of homology assigned to various substitutions, deletions and other modifications, including conservative amino acid substitutions. For instance, GCG contains programs such as “Gap” and “Bestfit” which can be used with default parameters to determine sequence homology or sequence identity between closely related polypeptides, such as homologous polypeptides from different species of organisms or between a wild type protein and a mutein thereof. See, e.g., GCG Version 6.1.

A typical algorithm when comparing a inhibitory molecule sequence to a database containing a large number of sequences from different organisms is the computer program BLAST (Altschul, 1990; Gish, 1993; Madden, 1996; Altschul, 1997; Zhang, 1997), especially blastp or tblastn (Altschul, 1997). Typical parameters for BLASTp are: Expectation value: (default); Filter: seg (default); Cost to open a gap: 11 (default); Cost to extend a gap: 1 (default); Max. alignments: 100 (default); Word size: 11 (default); No. of descriptions: 100 (default); Penalty Matrix: BLOWSUM62.

When searching a database containing sequences from a large number of different organisms, it is typical to compare amino acid sequences. Database searching using amino acid sequences can be measured by algorithms other than blastp known in the art. For instance, polypeptide sequences can be compared using FASTA, a program in GCG Version 6.1. FASTA provides alignments and percent sequence identity of the regions of the best overlap between the query and search sequences (Pearson, 1990, hereby incorporated herein by reference). For example, percent sequence identity between amino acid sequences can be determined using FASTA with its default parameters (a word size of 2 and the PAM250 scoring matrix), as provided in GCG Version 6.1, hereby incorporated herein by reference.

It is understood that the nucleic acid sequences described above include “genes” and that the nucleic acid molecules described above include “vectors” or “plasmids.” For example, a nucleic acid sequence encoding a keto thiolase can be encoded by an atoB gene or homolog thereof, or an fadA gene or homolog thereof. Accordingly, the term “gene”, also called a “structural gene” refers to a nucleic acid sequence that codes for a particular sequence of amino acids, which comprise all or part of one or more proteins or enzymes, and may include regulatory (non-transcribed) DNA sequences, such as promoter sequences, which determine for example the conditions under which the gene is expressed. The transcribed region of the gene may include untranslated regions, including introns, 5′-untranslated region (UTR), and 3′-UTR, as well as the coding sequence. The term “nucleic acid” or “recombinant nucleic acid” refers to polynucleotides such as deoxyribonucleic acid (DNA), and, where appropriate, ribonucleic acid (RNA). The term “expression” with respect to a gene sequence refers to transcription of the gene and, as appropriate, translation of the resulting mRNA transcript to a protein. Thus, as will be clear from the context, expression of a protein results from transcription and translation of the open reading frame sequence.

The term “operon” refers two or more genes which are transcribed as a single transcriptional unit from a common promoter. In some embodiments, the genes comprising the operon are contiguous genes. It is understood that transcription of an entire operon can be modified (i.e., increased, decreased, or eliminated) by modifying the common promoter. Alternatively, any gene or combination of genes in an operon can be modified to alter the function or activity of the encoded polypeptide. The modification can result in an increase in the activity of the encoded polypeptide. Further, the modification can impart new activities on the encoded polypeptide. Exemplary new activities include the use of alternative substrates and/or the ability to function in alternative environmental conditions.

A “vector” is any means by which a nucleic acid can be propagated and/or transferred between organisms, cells, or cellular components. Vectors include viruses, bacteriophage, pro-viruses, plasmids, phagemids, transposons, and artificial chromosomes such as YACs (yeast artificial chromosomes), BACs (bacterial artificial chromosomes), and PLACs (plant artificial chromosomes), and the like, that are “episomes,” that is, that replicate autonomously or can integrate into a chromosome of a host cell. A vector can also be a naked RNA polynucleotide, a naked DNA polynucleotide, a polynucleotide composed of both DNA and RNA within the same strand, a poly-lysine-conjugated DNA or RNA, a peptide-conjugated DNA or RNA, a liposome-conjugated DNA, or the like, that are not episomal in nature, or it can be an organism which comprises one or more of the above polynucleotide constructs such as an agrobacterium or a bacterium.

“Transformation” refers to the process by which a vector is introduced into a host cell. Transformation (or transduction, or transfection), can be achieved by any one of a number of means including electroporation, microinjection, biolistics (or particle bombardment-mediated delivery), or agrobacterium mediated transformation.

Those of skill in the art will recognize that, due to the degenerate nature of the genetic code, a variety of DNA compounds differing in their nucleotide sequences can be used to encode a given amino acid sequence of the disclosure. The native DNA sequence encoding the biosynthetic enzymes described above are referenced herein merely to illustrate an embodiment of the disclosure, and the disclosure includes DNA compounds of any sequence that encode the amino acid sequences of the polypeptides and proteins of the enzymes utilized in the methods of the disclosure. In similar fashion, a polypeptide can typically tolerate one or more amino acid substitutions, deletions, and insertions in its amino acid sequence without loss or significant loss of a desired activity. The disclosure includes such polypeptides with alternate amino acid sequences, and the amino acid sequences encoded by the DNA sequences shown herein merely illustrate embodiments of the disclosure.

The disclosure provides nucleic acid molecules in the form of recombinant DNA expression vectors or plasmids, as described in more detail below, that encode one or more target enzymes. Generally, such vectors can either replicate in the cytoplasm of the host microorganism or integrate into the chromosomal DNA of the host microorganism. In either case, the vector can be a stable vector (i.e., the vector remains present over many cell divisions, even if only with selective pressure) or a transient vector (i.e., the vector is gradually lost by host microorganisms with increasing numbers of cell divisions). The disclosure provides DNA molecules in isolated (i.e., not pure, but existing in a preparation in an abundance and/or concentration not found in nature) and purified (i.e., substantially free of contaminating materials or substantially free of materials with which the corresponding DNA would be found in nature) forms.

Provided herein are methods for the heterologous expression of one or more of the biosynthetic genes involved in 1-propanol, isobutanol, 1-butanol, 2-methyl 1-butanol, 3-methyl 1-butanol, and/or 2-phenylethanol biosynthesis and recombinant DNA expression vectors useful in the method. Thus, included within the scope of the disclosure are recombinant expression vectors that include such nucleic acids. The term expression vector refers to a nucleic acid that can be introduced into a host microorganism or cell-free transcription and translation system. An expression vector can be maintained permanently or transiently in a microorganism, whether as part of the chromosomal or other DNA in the microorganism or in any cellular compartment, such as a replicating vector in the cytoplasm. An expression vector also comprises a promoter that drives expression of an RNA, which typically is translated into a polypeptide in the microorganism or cell extract. For efficient translation of RNA into protein, the expression vector also typically contains a ribosome-binding site sequence positioned upstream of the start codon of the coding sequence of the gene to be expressed. Other elements, such as enhancers, secretion signal sequences, transcription termination sequences, and one or more marker genes by which host microorganisms containing the vector can be identified and/or selected, may also be present in an expression vector. Selectable markers, i.e., genes that confer antibiotic resistance or sensitivity, are used and confer a selectable phenotype on transformed cells when the cells are grown in an appropriate selective medium.

The various components of an expression vector can vary widely, depending on the intended use of the vector and the host cell(s) in which the vector is intended to replicate or drive expression. Expression vector components suitable for the expression of genes and maintenance of vectors in E. coli, yeast, Streptomyces, and other commonly used cells are widely known and commercially available. For example, suitable promoters for inclusion in the expression vectors of the disclosure include those that function in eukaryotic or prokaryotic host microorganisms. Promoters can comprise regulatory sequences that allow for regulation of expression relative to the growth of the host microorganism or that cause the expression of a gene to be turned on or off in response to a chemical or physical stimulus. For E. coli and certain other bacterial host cells, promoters derived from genes for biosynthetic enzymes, antibiotic-resistance conferring enzymes, and phage proteins can be used and include, for example, the galactose, lactose (lac), maltose, tryptophan (trp), beta-lactamase (bla), bacteriophage lambda PL, and T5 promoters. In addition, synthetic promoters, such as the tac promoter (U.S. Pat. No. 4,551,433), can also be used. For E. coli expression vectors, it is useful to include an E. coli origin of replication, such as from pUC, p1P, p1, and pBR.

Thus, recombinant expression vectors contain at least one expression system, which, in turn, is composed of at least a portion of PKS and/or other biosynthetic gene coding sequences operably linked to a promoter and optionally termination sequences that operate to effect expression of the coding sequence in compatible host cells. The host cells are modified by transformation with the recombinant DNA expression vectors of the disclosure to contain the expression system sequences either as extrachromosomal elements or integrated into the chromosome.

Due to the inherent degeneracy of the genetic code, other nucleic acid sequences which encode substantially the same or a functionally equivalent amino acid sequence can also be used to clone and express the polynucleotides encoding such enzymes. As previously noted, the term “host cell” is used interchangeably with the term “recombinant microorganism” and includes any cell type which is suitable for producing e.g., 1-propanol, isobutanol, 1-butanol, 2-methyl 1-butanol, 3-methyl 1-butanol and/or 2-phenylethanol and susceptible to transformation with a nucleic acid construct such as a vector or plasmid.

As will be understood by those of skill in the art, it can be advantageous to modify a coding sequence to enhance its expression in a particular host. The genetic code is redundant with 64 possible codons, but most organisms typically use a subset of these codons. The codons that are utilized most often in a species are called optimal codons, and those not utilized very often are classified as rare or low-usage codons. Codons can be substituted to reflect the preferred codon usage of the host, a process sometimes called “codon optimization” or “controlling for species codon bias.”

Optimized coding sequences containing codons preferred by a particular prokaryotic or eukaryotic host (see also, Murray et al. (1989) Nucl. Acids Res. 17:477-508) can be prepared, for example, to increase the rate of translation or to produce recombinant RNA transcripts having desirable properties, such as a longer half-life, as compared with transcripts produced from a non-optimized sequence. Translation stop codons can also be modified to reflect host preference. For example, typical stop codons for S. cerevisiae and mammals are UAA and UGA, respectively. The typical stop codon for monocotyledonous plants is UGA, whereas insects and E. coli commonly use UAA as the stop codon (Dalphin et al. (1996) Nucl. Acids Res. 24: 216-218). Methodology for optimizing a nucleotide sequence for expression in a plant is provided, for example, in U.S. Pat. No. 6,015,891, and the references cited therein.

A nucleic acid of the disclosure can be amplified using cDNA, mRNA or alternatively, genomic DNA, as a template and appropriate oligonucleotide primers according to standard PCR amplification techniques and those procedures described in the Examples section below. The nucleic acid so amplified can be cloned into an appropriate vector and characterized by DNA sequence analysis. Furthermore, oligonucleotides corresponding to nucleotide sequences can be prepared by standard synthetic techniques, e.g., using an automated DNA synthesizer.

It is also understood that an isolated nucleic acid molecule encoding a polypeptide homologous to the enzymes described herein can be created by introducing one or more nucleotide substitutions, additions or deletions into the nucleotide sequence encoding the particular polypeptide, such that one or more amino acid substitutions, additions or deletions are introduced into the encoded protein. Mutations can be introduced into the nucleic acid sequence by standard techniques, such as site-directed mutagenesis and PCR-mediated mutagenesis. In contrast to those positions where it may be desirable to make a non-conservative amino acid substitutions (see above), in some positions it is preferable to make conservative amino acid substitutions. A “conservative amino acid substitution” is one in which the amino acid residue is replaced with an amino acid residue having a similar side chain. Families of amino acid residues having similar side chains have been defined in the art. These families include amino acids with basic side chains (e.g., lysine, arginine, histidine), acidic side chains (e.g., aspartic acid, glutamic acid), uncharged polar side chains (e.g., glycine, asparagine, glutamine, serine, threonine, tyrosine, cysteine), nonpolar side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan), beta-branched side chains (e.g., threonine, valine, isoleucine) and aromatic side chains (e.g., tyrosine, phenylalanine, tryptophan, histidine).

In another embodiment a method for producing e.g., 1-propanol, isobutanol, 1-butanol, 2-methyl 1-butanol, 3-methyl 1-butanol or 2-phenylethanol is provided. The method includes culturing a recombinant photoautotroph microorganism(s) or culture comprising a photoautotroph and a recombinant non-photosynthetic or photoheterotroph microorganism as provided herein in the presence of a suitable substrate (e.g., CO₂) and under conditions suitable for the conversion of the substrate to 1-propanol, isobutanol, 1-butanol, 2-methyl 1-butanol, 3-methyl 1-butanol or 2-phenylethanol. The alcohol produced by a microorganism or culture provided herein can be detected by any method known to the skilled artisan. Culture conditions suitable for the growth and maintenance of a recombinant microorganism provided herein are described in the Examples below. The skilled artisan will recognize that such conditions can be modified to accommodate the requirements of each microorganism.

As previously discussed, general texts which describe molecular biological techniques useful herein, including the use of vectors, promoters and many other relevant topics, include Berger and Kimmel, Guide to Molecular Cloning Techniques, Methods in Enzymology Volume 152, (Academic Press, Inc., San Diego, Calif.) (“Berger”); Sambrook et al., Molecular Cloning—A Laboratory Manual, 2d ed., Vol. 1-3, Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y., 1989 (“Sambrook”) and Current Protocols in Molecular Biology, F. M. Ausubel et al., eds., Current Protocols, a joint venture between Greene Publishing Associates, Inc. and John Wiley & Sons, Inc., (supplemented through 1999) (“Ausubel”). Examples of protocols sufficient to direct persons of skill through in vitro amplification methods, including the polymerase chain reaction (PCR), the ligase chain reaction (LCR), Qβ-replicase amplification and other RNA polymerase mediated techniques (e.g., NASBA), e.g., for the production of the homologous nucleic acids of the disclosure are found in Berger, Sambrook, and Ausubel, as well as in Mullis et al. (1987) U.S. Pat. No. 4,683,202; Innis et al., eds. (1990) PCR Protocols: A Guide to Methods and Applications (Academic Press Inc. San Diego, Calif.) (“Innis”); Arnheim & Levinson (Oct. 1, 1990) C&EN 36-47; The Journal Of NIH Research (1991) 3: 81-94; Kwoh et al. (1989) Proc. Natl. Acad. Sci. USA 86: 1173; Guatelli et al. (1990) Proc. Nat'l. Acad. Sci. USA 87: 1874; Lomell et al. (1989) J. Clin. Chem. 35: 1826; Landegren et al. (1988) Science 241: 1077-1080; Van Brunt (1990) Biotechnology 8: 291-294; Wu and Wallace (1989) Gene 4:560; Barringer et al. (1990) Gene 89:117; and Sooknanan and Malek (1995) Biotechnology 13: 563-564. Improved methods for cloning in vitro amplified nucleic acids are described in Wallace et al., U.S. Pat. No. 5,426,039. Improved methods for amplifying large nucleic acids by PCR are summarized in Cheng et al. (1994) Nature 369: 684-685 and the references cited therein, in which PCR amplicons of up to 40 kb are generated. One of skill will appreciate that essentially any RNA can be converted into a double stranded DNA suitable for restriction digestion, PCR expansion and sequencing using reverse transcriptase and a polymerase. See, e.g., Ausubel, Sambrook and Berger, all supra.

The disclosure provides accession numbers for various genes, homologs and variants useful in the generation of recombinant microorganism described herein. It is to be understood that homologs and variants described herein are exemplary and non-limiting. Additional homologs, variants and sequences are available to those of skill in the art using various databases including, for example, the National Center for Biotechnology Information (NCBI) access to which is available on the World-Wide-Web.

Ethanol Dehydrogenase (also referred to as Aldehyde-alcohol dehydrogenase) is encoded in E. coli by adhE. adhE comprises three activities: alcohol dehydrogenase (ADH); acetaldehyde/acetyl-CoA dehydrogenase (ACDH); pyruvate-formate-lyase deactivase (PFL deactivase); PFL deactivase activity catalyzes the quenching of the pyruvate-formate-lyase catalyst in an iron, NAD, and CoA dependent reaction. Homologs are known in the art (see, e.g., aldehyde-alcohol dehydrogenase (Polytomella sp. Pringsheim 198.80) gi|40644910|emb|CAD42653.2|(40644910); aldehyde-alcohol dehydrogenase (Clostridium botulinum A str. ATCC 3502) gi|148378348|ref|YP_(—)001252889.1|(148378348); aldehyde-alcohol dehydrogenase (Yersinia pestis CO92) gi|16122410|ref|NP_(—)405723.1|(16122410); aldehyde-alcohol dehydrogenase (Yersinia pseudotuberculosis IP 32953) gi|51596429|ref|YP_(—)070620.1|(51596429); aldehyde-alcohol dehydrogenase (Yersinia pestis CO92) gi|115347889|emb|CAL20810.1|(115347889); aldehyde-alcohol dehydrogenase (Yersinia pseudotuberculosis IP 32953) gi|51589711|emb|CAH21341.1|(51589711); Aldehyde-alcohol dehydrogenase (Escherichia coli CFT073) gi|26107972|gb|AAN80172.1|AE016760_(—)31(26107972); aldehyde-alcohol dehydrogenase (Yersinia pestis biovar Microtus str. 91001) gi|45441777|ref|NP_(—)993316.1|(45441777); aldehyde-alcohol dehydrogenase (Yersinia pestis biovar Microtus str. 91001) gi|45436639|gb|AAS62193.1|(45436639); aldehyde-alcohol dehydrogenase (Clostridium perfringens ATCC 13124) gi|110798574|ref|YP_(—)697219.1|(110798574); aldehyde-alcohol dehydrogenase (Shewanella oneidensis MR-1)gi|24373696|ref|NP_(—)717739.1|(24373696); aldehyde-alcohol dehydrogenase (Clostridium botulinum A str. ATCC 19397) gi|153932445|ref|YP_(—)001382747.1|(153932445); aldehyde-alcohol dehydrogenase (Yersinia pestis biovar Antigua str. E1979001) gi|165991833|gb|EDR44134.1|(165991833); aldehyde-alcohol dehydrogenase (Clostridium botulinum A str. Hall) gi|153937530|ref|YP_(—)001386298.1|(153937530); aldehyde-alcohol dehydrogenase (Clostridium perfringens ATCC 13124) gi|110673221|gb|ABG82208.1|(110673221); aldehyde-alcohol dehydrogenase (Clostridium botulinum A str. Hall) gi|152933444|gb|ABS38943.1|(152933444); aldehyde-alcohol dehydrogenase (Yersinia pestis biovar Orientalis str. F1991016) gi|165920640|gb|EDR37888.1|(165920640); aldehyde-alcohol dehydrogenase (Yersinia pestis biovar Orientalis str. IP275)gi|165913933|gb|EDR32551.1|(165913933); aldehyde-alcohol dehydrogenase (Yersinia pestis Angola) gi|162419116|ref|YP_(—)001606617.1|(162419116); aldehyde-alcohol dehydrogenase (Clostridium botulinum F str. Langeland) gi|153940830|ref|YP_(—)001389712.1|(153940830); aldehyde-alcohol dehydrogenase (Escherichia coli HS) gi|157160746|ref|YP_(—)001458064.1|(157160746); aldehyde-alcohol dehydrogenase (Escherichia coli E24377A) gi|157155679|ref|YP_(—)001462491.1|(157155679); aldehyde-alcohol dehydrogenase (Yersinia enterocolitica subsp. enterocolitica 8081) gi|123442494|ref|YP_(—)001006472.1|(123442494); aldehyde-alcohol dehydrogenase (Synechococcus sp. JA-3-3Ab) gi|86605191|ref|YP_(—)473954.1|(86605191); aldehyde-alcohol dehydrogenase (Listeria monocytogenes str. 4b F2365) gi|46907864|ref|YP_(—)014253.1|(46907864); aldehyde-alcohol dehydrogenase (Enterococcus faecalis V583) gi|29375484|ref|NP_(—)814638.1|(29375484); aldehyde-alcohol dehydrogenase (Streptococcus agalactiae 2603V/R) gi|22536238|ref|NP_(—)687089.1|(22536238); aldehyde-alcohol dehydrogenase (Clostridium botulinum A str. ATCC 19397) gi|152928489|gb|ABS33989.1|(152928489); aldehyde-alcohol dehydrogenase (Escherichia coli E24377A) gi|157077709|gb|ABV17417.1|(157077709); aldehyde-alcohol dehydrogenase (Escherichia coli HS) gi|157066426|gb|ABV05681.1|(157066426); aldehyde-alcohol dehydrogenase (Clostridium botulinum F str. Langeland) gi|152936726|gb|ABS42224.1|(152936726); aldehyde-alcohol dehydrogenase (Yersinia pestis CA88-4125) gi|149292312|gb|EDM42386.1|(149292312); aldehyde-alcohol dehydrogenase (Yersinia enterocolitica subsp. enterocolitica 8081) gi|122089455|emb|CAL12303.1|(122089455); aldehyde-alcohol dehydrogenase (Chlamydomonas reinhardtii) gi|92084840|emb|CAF04128.1|(92084840); aldehyde-alcohol dehydrogenase (Synechococcus sp. JA-3-3Ab) gi|86553733|gb|ABC98691.1|(86553733); aldehyde-alcohol dehydrogenase (Shewanella oneidensis MR-1) gi|24348056|gb|AAN55183.1|AE015655_(—)9(24348056); aldehyde-alcohol dehydrogenase (Enterococcus faecalis V583) gi|29342944|gb|AAO80708.1|(29342944); aldehyde-alcohol dehydrogenase (Listeria monocytogenes str. 4b F2365) gi|46881133|gb|AAT04430.1|(46881133); aldehyde-alcohol dehydrogenase (Listeria monocytogenes str. 1/2a F6854) gi|47097587|ref|ZP_(—)00235115.1|(47097587); aldehyde-alcohol dehydrogenase (Listeria monocytogenes str. 4b H7858) gi|47094265|ref|ZP_(—)00231973.1|(47094265); aldehyde-alcohol dehydrogenase (Listeria monocytogenes str. 4b H7858) gi|47017355|gb|EAL08180.1|(47017355); aldehyde-alcohol dehydrogenase (Listeria monocytogenes str. 1/2a F6854) gi|47014034|gb|EAL05039.1|(47014034); aldehyde-alcohol dehydrogenase (Streptococcus agalactiae 2603V/R) gi|22533058|gb|AAM98961.1|AE014194_(—)6(22533058)p; aldehyde-alcohol dehydrogenase (Yersinia pestis biovar Antigua str. E1979001) gi|166009278|ref|ZP_(—)02230176.1|(166009278); aldehyde-alcohol dehydrogenase (Yersinia pestis biovar Orientalis str. IP275) gi|165938272|ref|ZP_(—)02226831.1|(165938272); aldehyde-alcohol dehydrogenase (Yersinia pestis biovar Orientalis str. F1991016) gi|165927374|ref|ZP_(—)02223206.1|(165927374); aldehyde-alcohol dehydrogenase (Yersinia pestis Angola) gi|162351931|gb|ABX85879.1|(162351931); aldehyde-alcohol dehydrogenase (Yersinia pseudotuberculosis IP 31758) gi|153949366|ref|YP_(—)001400938.1|(153949366); aldehyde-alcohol dehydrogenase (Yersinia pseudotuberculosis IP 31758) gi|152960861|gb|ABS48322.1|(152960861); aldehyde-alcohol dehydrogenase (Yersinia pestis CA88-4125) gi|149365899|ref|ZP_(—)01887934.1|(149365899); Acetaldehyde dehydrogenase (acetylating) (Escherichia coli CFT073) gi|26247570|ref|NP_(—)753610.1|(26247570); aldehyde-alcohol dehydrogenase (includes: alcohol dehydrogenase; acetaldehyde dehydrogenase (acetylating) (EC 1.2.1.10) (acdh); pyruvate-formate-lyase deactivase (pfl deactivase)) (Clostridium botulinum A str. ATCC 3502) gi|148287832|emb|CAL81898.1|(148287832); aldehyde-alcohol dehydrogenase (Includes: Alcohol dehydrogenase (ADH); Acetaldehyde dehydrogenase (acetylating) (ACDH); Pyruvate-formate-lyase deactivase (PFL deactivase)) gi|71152980|sp|P0A9Q7.2|ADHE_ECOLI(71152980); aldehyde-alcohol dehydrogenase (includes: alcohol dehydrogenase and acetaldehyde dehydrogenase, and pyruvate-formate-lyase deactivase (Erwinia carotovora subsp. atroseptica SCRI1043) gi|50121254|ref|YP_(—)050421.1|(50121254); aldehyde-alcohol dehydrogenase (includes: alcohol dehydrogenase and acetaldehyde dehydrogenase, and pyruvate-formate-lyase deactivase (Erwinia carotovora subsp. atroseptica SCRI1043) gi|49611780|emb|CAG75229.1|(49611780); Aldehyde-alcohol dehydrogenase (Includes: Alcohol dehydrogenase (ADH); Acetaldehyde dehydrogenase (acetylating) (ACDH)) gi|19858620|sp|P33744.3|ADHE_CLOAB(19858620); Aldehyde-alcohol dehydrogenase (Includes: Alcohol dehydrogenase (ADH); Acetaldehyde dehydrogenase (acetylating) (ACDH); Pyruvate-formate-lyase deactivase (PFL deactivase)) gi|71152683|sp|P0A9Q8.2|ADHE_ECO57(71152683); aldehyde-alcohol dehydrogenase (includes: alcohol dehydrogenase; acetaldehyde dehydrogenase (acetylating); pyruvate-formate-lyase deactivase (Clostridium difficile 630) gi|126697906|ref|YP_(—)001086803.1|(126697906); aldehyde-alcohol dehydrogenase (includes: alcohol dehydrogenase; acetaldehyde dehydrogenase (acetylating); pyruvate-formate-lyase deactivase (Clostridium difficile 630) gi|115249343|emb|CAJ67156.1|(115249343); Aldehyde-alcohol dehydrogenase (includes: alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (acetylating) (ACDH); pyruvate-formate-lyase deactivase (PFL deactivase)) (Photorhabdus luminescens subsp. laumondii TTO1) gi|37526388|ref|NP_(—)929732.1|(37526388); aldehyde-alcohol dehydrogenase 2 (includes: alcohol dehydrogenase; acetaldehyde dehydrogenase) (Streptococcus pyogenes str. Manfredo) gi|134271169|emb|CAM29381.1|(134271169); Aldehyde-alcohol dehydrogenase (includes: alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (acetylating) (ACDH); pyruvate-formate-lyase deactivase (PFL deactivase)) (Photorhabdus luminescens subsp. laumondii TTO1) gi|36785819|emb|CAE14870.1|(36785819); aldehyde-alcohol dehydrogenase (includes: alcohol dehydrogenase and pyruvate-formate-lyase deactivase (Clostridium difficile 630) gi|126700586|ref|YP_(—)001089483.1|(126700586); aldehyde-alcohol dehydrogenase (includes: alcohol dehydrogenase and pyruvate-formate-lyase deactivase (Clostridium difficile 630) gi|115252023|emb|CAJ69859.1|(115252023); aldehyde-alcohol dehydrogenase 2 (Streptococcus pyogenes str. Manfredo) gi|139472923|ref|YP_(—)001127638.1|(139472923); aldehyde-alcohol dehydrogenase E (Clostridium perfringens str. 13) gi|18311513|ref|NP_(—)563447.1|(18311513); aldehyde-alcohol dehydrogenase E (Clostridium perfringens str. 13) gi|18146197|dbj|BAB82237.1|(18146197); Aldehyde-alcohol dehydrogenase, ADHE1 (Clostridium acetobutylicum ATCC 824) gi|15004739|ref|NP_(—)149199.1|(15004739); Aldehyde-alcohol dehydrogenase, ADHE1 (Clostridium acetobutylicum ATCC 824) gi|14994351|gb|AAK76781.1|AE001438_(—)34(14994351); Aldehyde-alcohol dehydrogenase 2 (Includes: Alcohol dehydrogenase (ADH); acetaldehyde/acetyl-CoA dehydrogenase (ACDH)) gi|2492737|sp|Q24803.1|ADH2_ENTHI(2492737); alcohol dehydrogenase (Salmonella enterica subsp. enterica serovar Typhi str. CT18) gi|16760134|ref|NP_(—)455751.1|(16760134); and alcohol dehydrogenase (Salmonella enterica subsp. enterica serovar Typhi) gi|16502428|emb|CAD08384.1|(16502428)), each sequence associated with the accession number is incorporated herein by reference in its entirety.

Lactate Dehydrogenase (also referred to as D-lactate dehydrogenase and fermentive dehydrognase) is encoded in E. coli by ldhA and catalyzes the NADH-dependent conversion of pyruvate to D-lactate. ldhA homologs and variants are known. In fact there are currently 1664 bacterial lactate dehydrogenases available through NCBI. For example, such homologs and variants include, for example, D-lactate dehydrogenase (D-LDH) (Fermentative lactate dehydrogenase) gi|1730102|sp|P52643.1|LDHD_ECOLI(1730102); D-lactate dehydrogenase gi|1049265|gb|AAB51772.1|(1049265); D-lactate dehydrogenase (Escherichia coli APEC O1) gi|117623655|ref|YP_(—)852568.1|(117623655); D-lactate dehydrogenase (Escherichia coli CFT073) gi|26247689|ref|NP_(—)753729.1|(26247689); D-lactate dehydrogenase (Escherichia coli O157:H7 EDL933) gi|15801748|ref|NP_(—)287766.1|(15801748); D-lactate dehydrogenase (Escherichia coli APEC O1) gi|115512779|gb|ABJ00854.1|(115512779); D-lactate dehydrogenase (Escherichia coli CFT073) gi|26108091|gb|AAN80291.1|AE016760_(—)150(26108091); fermentative D-lactate dehydrogenase, NAD-dependent (Escherichia coli K12) gi|16129341|ref|NP_(—)415898.1|(16129341); fermentative D-lactate dehydrogenase, NAD-dependent (Escherichia coli UTI89) gi|91210646|ref|YP_(—)540632.1|(91210646); fermentative D-lactate dehydrogenase, NAD-dependent (Escherichia coli K12) gi|1787645|gb|AAC74462.1|(1787645); fermentative D-lactate dehydrogenase, NAD-dependent (Escherichia coli W3110) gi|89108227|ref|AP_(—)002007.1|(89108227); fermentative D-lactate dehydrogenase, NAD-dependent (Escherichia coli W3110) gi|1742259|dbj|BAA14990.1|(1742259); fermentative D-lactate dehydrogenase, NAD-dependent (Escherichia coli UTI89) gi|91072220|gb|ABE07101.1|(91072220); fermentative D-lactate dehydrogenase, NAD-dependent (Escherichia coli O157:H7 EDL933) gi|12515320|gb|AAG56380.1|AE005366_(—)6(12515320); fermentative D-lactate dehydrogenase (Escherichia coli O157:H7 str. Sakai) gi|13361468|dbj|BAB35425.1|(13361468); COG1052: Lactate dehydrogenase and related dehydrogenases (Escherichia coli 101-1) gi|83588593|ref|ZP_(—)00927217.1|(83588593); COG1052: Lactate dehydrogenase and related dehydrogenases (Escherichia coli 53638) gi|75515985|ref|ZP_(—)00738103.1|(75515985); COG1052: Lactate dehydrogenase and related dehydrogenases (Escherichia coli E22) gi|75260157|ref|ZP_(—)00731425.1|(75260157); COG1052: Lactate dehydrogenase and related dehydrogenases (Escherichia coli F11) gi|75242656|ref|ZP_(—)00726400.1|(75242656); COG1052: Lactate dehydrogenase and related dehydrogenases (Escherichia coli E110019) gi|75237491|ref|ZP_(—)00721524.1|(75237491); COG1052: Lactate dehydrogenase and related dehydrogenases (Escherichia coli B7A) gi|75231601|ref|ZP_(—)00717959.1|(75231601); and COG1052: Lactate dehydrogenase and related dehydrogenases (Escherichia coli B171) gi|75211308|ref|ZP_(—)00711407.1|(75211308), each sequence associated with the accession number is incorporated herein by reference in its entirety.

Two membrane-bound, FAD-containing enzymes are responsible for the catalysis of fumarate and succinate interconversion; the fumarate reductase is used in anaerobic growth, and the succinate dehydrogenase is used in aerobic growth. Fumarate reductase comprises multiple subunits (e.g., frdA, B, and C in E. coli). Modification of any one of the subunits can result in the desired activity herein. For example, a knockout of frdB, frdC or frdBC is useful in the methods of the disclosure. Frd homologs and variants are known. For example, homologs and variants includes, for example, Fumarate reductase subunit D (Fumarate reductase 13 kDa hydrophobic protein) gi|67463543|sp|P0A8Q3.1|FRDD_ECOLI(67463543); Fumarate reductase subunit C (Fumarate reductase 15 kDa hydrophobic protein) gi|1346037|sp|P20923.2|FRDC_PROVU(1346037); Fumarate reductase subunit D (Fumarate reductase 13 kDa hydrophobic protein) gi|120499|sp|P20924.1|FRDD_PROVU(120499); Fumarate reductase subunit C (Fumarate reductase 15 kDa hydrophobic protein) gi|67463538|sp|P0A8Q0.1|FRDC_ECOLI(67463538); fumarate reductase iron-sulfur subunit (Escherichia coli) gi|145264|gb|AAA23438.1|(145264); fumarate reductase flavoprotein subunit (Escherichia coli) gi|145263|gb|AAA23437.1|(145263); Fumarate reductase flavoprotein subunit gi|37538290|sp|P17412.3|FRDA_WOLSU(37538290); Fumarate reductase flavoprotein subunit gi|120489|sp|P00363.3|FRDA_ECOLI(120489); Fumarate reductase flavoprotein subunit gi|120490|sp|P20922.1|FRDA_PROVU(120490); Fumarate reductase flavoprotein subunit precursor (Flavocytochrome c) (Flavocytochrome c3) (Fcc3) gi|119370087|sp|Q07WU7.2|FRDA_SHEFN(119370087); Fumarate reductase iron-sulfur subunit gi|81175308|sp|P0AC47.2|FRDB_ECOLI(81175308); Fumarate reductase flavoprotein subunit (Flavocytochrome c) (Flavocytochrome c3) (Fcc3) gi|119370088|sp|P0C278.1|FRDA_SHEFR(119370088); Frd operon uncharacterized protein C gi|140663|sp|P20927.1|YFRC_PROVU(140663); Frd operon probable iron-sulfur subunit A gi|140661|sp|P20925.1|YFRA_PROVU(140661); Fumarate reductase iron-sulfur subunit gi|120493|sp|P20921.2|FRDB_PROVU(120493); Fumarate reductase flavoprotein subunit gi|2494617|sp|O06913.2|FRDA_HELPY(2494617); Fumarate reductase flavoprotein subunit precursor (Iron(III)-induced flavocytochrome C3) (Ifc3) gi|13878499|sp|Q9Z4P0.1|FRD2_SHEFN(13878499); Fumarate reductase flavoprotein subunit gi|54041009|sp|P64174.1|FRDA_MYCTU(54041009); Fumarate reductase flavoprotein subunit gi|54037132|sp|P64175.1|FRDA_MYCBO(54037132); Fumarate reductase flavoprotein subunit gi|12230114|sp|Q9ZMP0.1|FRDA_HELPJ(12230114); Fumarate reductase flavoprotein subunit gi|1169737|sp|P44894.1|FRDA_HAEIN(1169737); fumarate reductase flavoprotein subunit (Wolinella succinogenes) gi|13160058|emb|CAA04214.2|(13160058); Fumarate reductase flavoprotein subunit precursor (Flavocytochrome c) (FL cyt) gi|25452947|sp|P83223.2|FRDA_SHEON(25452947); fumarate reductase iron-sulfur subunit (Wolinella succinogenes) gi|2282000|emb|CAA04215.1|(2282000); and fumarate reductase cytochrome b subunit (Wolinella succinogenes) gi|2281998|emb|CAA04213.1|(2281998), each sequence associated with the accession number is incorporated herein by reference in its entirety.

Acetate kinase is encoded in E. coli by ackA. AckA is involved in conversion of acetyl-coA to acetate. Specifically, ackA catalyzes the conversion of acetyl-phophate to acetate. AckA homologs and variants are known. The NCBI database list approximately 1450 polypeptides as bacterial acetate kinases. For example, such homologs and variants include acetate kinase (Streptomyces coelicolor A3(2)) gi|21223784|ref|NP_(—)629563.1|(21223784); acetate kinase (Streptomyces coelicolor A3(2)) gi|6808417|emb|CAB70654.1|(6808417); acetate kinase (Streptococcus pyogenes M1 GAS) gi|15674332|ref|NP_(—)268506.1|(15674332); acetate kinase (Campylobacter jejuni subsp. jejuni NCTC 11168) gi|15792038|ref|NP_(—)281861.1|(15792038); acetate kinase (Streptococcus pyogenes M1 GAS) gi|13621416|gb|AAK33227.1|(13621416); acetate kinase (Rhodopirellula baltica SH 1) gi|32476009|ref|NP_(—)869003.1|(32476009); acetate kinase (Rhodopirellula baltica SH 1) gi|32472045|ref|NP_(—)865039.1|(32472045); acetate kinase (Campylobacter jejuni subsp. jejuni NCTC 11168) gi|112360034|emb|CAL34826.1|(112360034); acetate kinase (Rhodopirellula baltica SH 1) gi|32446553|emb|CAD76388.1|(32446553); acetate kinase (Rhodopirellula baltica SH 1) gi|32397417|emb|CAD72723.1|(32397417); AckA (Clostridium kluyveri DSM 555) gi|153954016|ref|YP_(—)001394781.1|(153954016); acetate kinase (Bifidobacterium longum NCC2705) gi|23465540|ref|NP_(—)696143.1|(23465540); AckA (Clostridium kluyveri DSM 555) gi|46346897|gb|EDK33433.1|(146346897); Acetate kinase (Corynebacterium diphtheriae) gi|38200875|emb|CAE50580.1|(38200875); acetate kinase (Bifidobacterium longum NCC2705) gi|23326203|gb|AAN24779.1|(23326203); Acetate kinase (Acetokinase) gi|67462089|sp|P0A6A3.1|ACKA_ECOLI(67462089); and AckA (Bacillus licheniformis DSM 13) gi|52349315|gb|AAU41949.1|(52349315), the sequences associated with such accession numbers are incorporated herein by reference.

Phosphate acetyltransferase is encoded in E. coli by pta. PTA is involved in conversion of acetate to acetyl-CoA. Specifically, PTA catalyzes the conversion of acetyl-coA to acetyl-phosphate. PTA homologs and variants are known. There are approximately 1075 bacterial phosphate acetyltransferases available on NCBI. For example, such homologs and variants include phosphate acetyltransferase Pta (Rickettsia felis URRWXCal2) gi|67004021|gb|AAY60947.1|(67004021); phosphate acetyltransferase (Buchnera aphidicola str. Cc (Cinara cedri)) gi|116256910|gb|ABJ90592.1|(116256910); pta (Buchnera aphidicola str. Cc (Cinara cedri)) gi|116515056|ref|YP_(—)802685.1|(116515056); pta (Wigglesworthia glossinidia endosymbiont of Glossina brevipalpis) gi|25166135|dbj|BAC24326.1|(25166135); Pta (Pasteurella multocida subsp. multocida str. Pm70) gi|12720993|gb|AAK02789.1|(12720993); Pta (Rhodospirillum rubrum) gi|25989720|gb|AAN75024.1|(25989720); pta (Listeria welshimeri serovar 6b str. SLCC5334) gi|116742418|emb|CAK21542.1|(116742418); Pta (Mycobacterium avium subsp. paratuberculosis K-10) gi|41398816|gb|AAS06435.1|(41398816); phosphate acetyltransferase (pta) (Borrelia burgdorferi B31) gi|15594934|ref|NP_(—)212723.1|(15594934); phosphate acetyltransferase (pta) (Borrelia burgdorferi B31) gi|2688508|gb|AAB91518.1|(2688508); phosphate acetyltransferase (pta) (Haemophilus influenzae Rd KW20) gi|1574131|gb|AAC22857.1|(1574131); Phosphate acetyltransferase Pta (Rickettsia bellii RML369-C) gi|91206026|ref|YP_(—)538381.1|(91206026); Phosphate acetyltransferase Pta (Rickettsia bellii RML369-C) gi|91206025|ref|YP_(—)538380.1|(91206025); phosphate acetyltransferase pta (Mycobacterium tuberculosis F11) gi|148720131|gb|ABR04756.1|(148720131); phosphate acetyltransferase pta (Mycobacterium tuberculosis str. Haarlem) gi|134148886|gb|EBA40931.1|(134148886); phosphate acetyltransferase pta (Mycobacterium tuberculosis C) gi|124599819|gb|EAY58829.1|(124599819); Phosphate acetyltransferase Pta (Rickettsia bellii RML369-C) gi|91069570|gb|ABE05292.1|(91069570); Phosphate acetyltransferase Pta (Rickettsia bellii RML369-C) gi|91069569|gb|ABE05291.1|(91069569); phosphate acetyltransferase (pta) (Treponema pallidum subsp. pallidum str. Nichols) gi|5639088|ref|NP_(—)218534.1|(15639088); and phosphate acetyltransferase (pta) (Treponema pallidum subsp. pallidum str. Nichols) gi|3322356|gb|AAC65090.1|(3322356), each sequence associated with the accession number is incorporated herein by reference in its entirety.

Pyruvate-formate lyase (Formate acetylytransferase) is an enzyme that catalyzes the conversion of pyruvate to acetly-coA and formate. It is induced by pfl-activating enzyme under anaerobic conditions by generation of an organic free radical and decreases significantly during phosphate limitation. Formate acetylytransferase is encoded in E. coli by pflB. PFLB homologs and variants are known. For examples, such homologs and variants include, for example, Formate acetyltransferase 1 (Pyruvate formate-lyase 1) gi|129879|sp|P09373.2|PFLB_ECOLI(129879); formate acetyltransferase 1 (Yersinia pestis CO92) gi|16121663|ref|NP_(—)404976.1|(16121663); formate acetyltransferase 1 (Yersinia pseudotuberculosis IP 32953) gi|51595748|ref|YP_(—)069939.1|(51595748); formate acetyltransferase 1 (Yersinia pestis biovar Microtus str. 91001) gi|45441037|ref|NP_(—)992576.1|(45441037); formate acetyltransferase 1 (Yersinia pestis CO92) gi|115347142|emb|CAL20035.1|(115347142); formate acetyltransferase 1 (Yersinia pestis biovar Microtus str. 91001) gi|45435896|gb|AAS61453.1|(45435896); formate acetyltransferase 1 (Yersinia pseudotuberculosis IP 32953) gi|51589030|emb|CAH20648.1|(51589030); formate acetyltransferase 1 (Salmonella enterica subsp. enterica serovar Typhi str. CT18) gi|16759843|ref|NP_(—)455460.1|(16759843); formate acetyltransferase 1 (Salmonella enterica subsp. enterica serovar Paratyphi A str. ATCC 9150) gi|56413977|ref|YP_(—)151052.1|(56413977); formate acetyltransferase 1 (Salmonella enterica subsp. enterica serovar Typhi) gi|16502136|emb|CAD05373.1|(16502136); formate acetyltransferase 1 (Salmonella enterica subsp. enterica serovar Paratyphi A str. ATCC 9150) gi|56128234|gb|AAV77740.1|(56128234); formate acetyltransferase 1 (Shigella dysenteriae Sd197) gi|82777577|ref|YP_(—)403926.1|(82777577); formate acetyltransferase 1 (Shigella flexneri 2a str. 2457T) gi|30062438|ref|NP_(—)836609.1|(30062438); formate acetyltransferase 1 (Shigella flexneri 2a str. 2457T) gi|30040684|gb|AAP16415.1|(30040684); formate acetyltransferase 1 (Shigella flexneri 5 str. 8401) gi|110614459|gb|ABF03126.1|(110614459); formate acetyltransferase 1 (Shigella dysenteriae Sd197) gi|81241725|gb|ABB62435.1|(81241725); formate acetyltransferase 1 (Escherichia coli O157:H7 EDL933) gi|12514066|gb|AAG55388.1|AE005279_(—)8(12514066); formate acetyltransferase 1 (Yersinia pestis KIM) gi|22126668|ref|NP_(—)670091.1|(22126668); formate acetyltransferase 1 (Streptococcus agalactiae A909) gi|76787667|ref|YP_(—)330335.1|(76787667); formate acetyltransferase 1 (Yersinia pestis KIM) gi|21959683|gb|AAM86342.1|AE013882_(—)3(21959683); formate acetyltransferase 1 (Streptococcus agalactiae A909) gi|76562724|gb|ABA45308.1|(76562724); formate acetyltransferase 1 (Yersinia enterocolitica subsp. enterocolitica 8081) gi|123441844|ref|YP_(—)001005827.1|(123441844); formate acetyltransferase 1 (Shigella flexneri 5 str. 8401) gi|110804911|ref|YP_(—)688431.1|(110804911); formate acetyltransferase 1 (Escherichia coli UTI89) gi|91210004|ref|YP_(—)539990.1|(91210004); formate acetyltransferase 1 (Shigella boydii Sb227) gi|82544641|ref|YP_(—)408588.1|(82544641); formate acetyltransferase 1 (Shigella sonnei Ss046) gi|74311459|ref|YP_(—)309878.1|(74311459); formate acetyltransferase 1 (Klebsiella pneumoniae subsp. pneumoniae MGH 78578) gi|152969488|ref|YP_(—)001334597.1|(152969488); formate acetyltransferase 1 (Salmonella enterica subsp. enterica serovar Typhi Ty2) gi|29142384|ref|NP_(—)805726.1|(29142384) formate acetyltransferase 1 (Shigella flexneri 2a str. 301) gi|24112311|ref|NP_(—)706821.1|(24112311); formate acetyltransferase 1 (Escherichia coli O157:H7 EDL933) gi|15800764|ref|NP_(—)286778.1|(15800764); formate acetyltransferase 1 (Klebsiella pneumoniae subsp. pneumoniae MGH 78578) gi|150954337|gb|ABR76367.1|(150954337); formate acetyltransferase 1 (Yersinia pestis CA88-4125) gi|149366640|ref|ZP_(—)01888674.1|(149366640); formate acetyltransferase 1 (Yersinia pestis CA88-4125) gi|149291014|gb|EDM41089.1|(149291014); formate acetyltransferase 1 (Yersinia enterocolitica subsp. enterocolitica 8081) gi|122088805|emb|CAL11611.1|(122088805); formate acetyltransferase 1 (Shigella sonnei Ss046) gi|73854936|gb|AAZ87643.1|(73854936); formate acetyltransferase 1 (Escherichia coli UTI89) gi|91071578|gb|ABE06459.1|(91071578); formate acetyltransferase 1 (Salmonella enterica subsp. enterica serovar Typhi Ty2) gi|29138014|gb|AAO69575.1|(29138014); formate acetyltransferase 1 (Shigella boydii Sb227) gi|81246052|gb|ABB66760.1|(81246052); formate acetyltransferase 1 (Shigella flexneri 2a str. 301) gi|24051169|gb|AAN42528.1|(24051169); formate acetyltransferase 1 (Escherichia coli O157:H7 str. Sakai) gi|13360445|dbj|BAB34409.1|(13360445); formate acetyltransferase 1 (Escherichia coli O157:H7 str. Sakai) gi|15830240|ref|NP_(—)309013.1|(15830240); formate acetyltransferase I (pyruvate formate-lyase 1) (Photorhabdus luminescens subsp. laumondii TTO1) gi|36784986|emb|CAE13906.1|(36784986); formate acetyltransferase I (pyruvate formate-lyase 1) (Photorhabdus luminescens subsp. laumondii TTO1) gi|37525558|ref|NP_(—)928902.1|(37525558); formate acetyltransferase (Staphylococcus aureus subsp. aureus Mu50) gi|14245993|dbj|BAB56388.1|(14245993); formate acetyltransferase (Staphylococcus aureus subsp. aureus Mu50) gi|15923216|ref|NP_(—)370750.1|(15923216); Formate acetyltransferase (Pyruvate formate-lyase) gi|81706366|sp|Q7A7X6.1|PFLB_STAAN(81706366); Formate acetyltransferase (Pyruvate formate-lyase) gi|81782287|sp|Q99WZ7.1|PFLB_STAAM(81782287); Formate acetyltransferase (Pyruvate formate-lyase) gi|81704726|sp|Q7A1W9.1|PFLB_STAAW(81704726); formate acetyltransferase (Staphylococcus aureus subsp. aureus Mu3) gi|156720691|dbj|BAF77108.1|(156720691); formate acetyltransferase (Erwinia carotovora subsp. atroseptica SCRI1043) gi|50121521|ref|YP_(—)050688.1|(50121521); formate acetyltransferase (Erwinia carotovora subsp. atroseptica SCRI1043) gi|49612047|emb|CAG75496.1|(49612047); formate acetyltransferase (Staphylococcus aureus subsp. aureus str. Newman) gi|150373174|dbj|BAF66434.1|(150373174); formate acetyltransferase (Shewanella oneidensis MR-1) gi|24374439|ref|NP_(—)718482.1|(24374439); formate acetyltransferase (Shewanella oneidensis MR-1) gi|24349015|gb|AAN55926.1|AE015730_(—)3(24349015); formate acetyltransferase (Actinobacillus pleuropneumoniae serovar 3 str. JL03) gi|165976461|ref|YP_(—)001652054.1|(165976461); formate acetyltransferase (Actinobacillus pleuropneumoniae serovar 3 str. JL03) gi|165876562|gb|ABY69610.1|(165876562); formate acetyltransferase (Staphylococcus aureus subsp. aureus MW2) gi|21203365|dbj|BAB94066.1|(21203365); formate acetyltransferase (Staphylococcus aureus subsp. aureus N315) gi|13700141|dbj|BAB41440.1|(13700141); formate acetyltransferase (Staphylococcus aureus subsp. aureus str. Newman) gi|151220374|ref|YP_(—)001331197.1|(151220374); formate acetyltransferase (Staphylococcus aureus subsp. aureus Mu3) gi|156978556|ref|YP_(—)001440815.1|(156978556); formate acetyltransferase (Synechococcus sp. JA-2-3B′ a(2-13)) gi|86607744|ref|YP_(—)476506.1|(86607744); formate acetyltransferase (Synechococcus sp. JA-3-3Ab) gi|86605195|ref|YP_(—)473958.1|(86605195); formate acetyltransferase (Streptococcus pneumoniae D39) gi|116517188|ref|YP_(—)815928.1|(116517188); formate acetyltransferase (Synechococcus sp. JA-2-3B′ a(2-13)) gi|86556286|gb|ABD01243.1|(86556286); formate acetyltransferase (Synechococcus sp. JA-3-3Ab) gi|86553737|gb|ABC98695.1|(86553737); formate acetyltransferase (Clostridium novyi NT) gi|118134908|gb|ABK61952.1|(118134908); formate acetyltransferase (Staphylococcus aureus subsp. aureus MRSA252) gi|49482458|ref|YP_(—)039682.1|(49482458); and formate acetyltransferase (Staphylococcus aureus subsp. aureus MRSA252) gi|49240587|emb|CAG39244.1|(49240587), each sequence associated with the accession number is incorporated herein by reference in its entirety.

Alpha isopropylmalate synthase (EC 2.3.3.13, sometimes referred to a 2-isopropylmalate synthase, alpha-IPM synthetase) catalyzes the condensation of the acetyl group of acetyl-CoA with 3-methyl-2-oxobutanoate (2-oxoisovalerate) to form 3-carboxy-3-hydroxy-4-methylpentanoate (2-isopropylmalate). Alpha isopropylmalate synthase is encoded in E. coli by leuA. LeuA homologs and variants are known. For example, such homologs and variants include, for example, 2-isopropylmalate synthase (Corynebacterium glutamicum) gi|452382|emb|CAA50295.1|(452382); 2-isopropylmalate synthase (Escherichia coli K12) gi|16128068|ref|NP_(—)414616.1|(16128068); 2-isopropylmalate synthase (Escherichia coli K12) gi|1786261|gb|AAC73185.1|(1786261); 2-isopropylmalate synthase (Arabidopsis thaliana) gi|15237194|ref|NP_(—)197692.1|(15237194); 2-isopropylmalate synthase (Arabidopsis thaliana) gi|42562149|ref|NP_(—)173285.2|(42562149); 2-isopropylmalate synthase (Arabidopsis thaliana) gi|15221125|ref|NP_(—)177544.1|(15221125); 2-isopropylmalate synthase (Streptomyces coelicolor A3(2)) gi|32141173|ref|NP_(—)733575.1|(32141173); 2-isopropylmalate synthase (Rhodopirellula baltica SH 1) gi|32477692|ref|NP_(—)870686.1|(32477692); 2-isopropylmalate synthase (Rhodopirellula baltica SH 1) gi|32448246|emb|CAD77763.1|(32448246); 2-isopropylmalate synthase (Akkermansia muciniphila ATCC BAA-835) gi|166241432|gb|EDR53404.1|(166241432); 2-isopropylmalate synthase (Herpetosiphon aurantiacus ATCC 23779) gi|159900959|ref|YP_(—)001547206.1|(159900959); 2-isopropylmalate synthase (Dinoroseobacter shibae DFL 12) gi|159043149|ref|YP_(—)001531943.1|(159043149); 2-isopropylmalate synthase (Salinispora arenicola CNS-205) gi|159035933|ref|YP_(—)001535186.1|(159035933); 2-isopropylmalate synthase (Clavibacter michiganensis subsp. michiganensis NCPPB 382) gi|148272757|ref|YP_(—)001222318.1|(148272757); 2-isopropylmalate synthase (Escherichia coli B) gi|124530643|ref|ZP_(—)01701227.1|(124530643); 2-isopropylmalate synthase (Escherichia coli C str. ATCC 8739) gi|124499067|gb|EAY46563.1|(124499067); 2-isopropylmalate synthase (Bordetella pertussis Tohama I) gi|33591386|ref|NP_(—)879030.1|(33591386); 2-isopropylmalate synthase (Polynucleobacter necessarius STIR1) gi|164564063|ref|ZP_(—)02209880.1|(164564063); 2-isopropylmalate synthase (Polynucleobacter necessarius STIR1) gi|164506789|gb|EDQ94990.1|(164506789); and 2-isopropylmalate synthase (Bacillus weihenstephanensis KBAB4) gi|163939313|ref|YP_(—)001644197.1|(163939313), any sequence associated with the accession number is incorporated herein by reference in its entirety.

BCAA aminotransferases catalyze the formation of branched chain amino acids (BCAA). A number of such aminotranferases are known and are exemplified by ilvE in E. coli. Exemplary homologs and variants include sequences designated by the following accession numbers: ilvE (Microcystis aeruginosa PCC 7806) gi|159026756|emb|CAO86637.1|(159026756); IlvE (Escherichia coli) gi|87117962|gb|ABD20288.1|(87117962); IlvE (Escherichia coli) gi|87117960|gb|ABD20287.1|(87117960); IlvE (Escherichia coli) gi|87117958|gb|ABD20286.1|(87117958); IlvE (Shigella flexneri) gi|87117956|gb|ABD20285.1|(87117956); IlvE (Shigella flexneri) gi|87117954|gb|ABD20284.1|(87117954); IlvE (Shigella flexneri) gi|87117952|gb|ABD20283.1|(87117952); IlvE (Shigella flexneri) gi|87117950|gb|ABD20282.1|(87117950); IlvE (Shigella flexneri) gi|87117948|gb|ABD20281.1|(87117948); IlvE (Shigella flexneri) gi|87117946|gb|ABD20280.1|(87117946); IlvE (Shigella flexneri) gi|87117944|gb|ABD20279.1|(87117944); IlvE (Shigella flexneri) gi|87117942|gb|ABD20278.1|(87117942); IlvE (Shigella flexneri) gi|87117940|gb|ABD20277.1|(87117940); IlvE (Shigella flexneri) gi|87117938|gb|ABD20276.1|(87117938); IlvE (Shigella dysenteriae) gi|87117936|gb|ABD20275.1|(87117936); IlvE (Shigella dysenteriae) gi|87117934|gb|ABD20274.1|(87117934); IlvE (Shigella dysenteriae) gi|87117932|gb|ABD20273.1|(87117932); IlvE (Shigella dysenteriae) gi|87117930|gb|ABD20272.1|(87117930); and IlvE (Shigella dysenteriae) gi|87117928|gb|ABD20271.1|(87117928), each sequence associated with the accession number is incorporated herein by reference.

Tyrosine aminotransferases catalyzes transamination for both dicarboxylic and aromatic amino-acid substrates. A tyrosine aminotransferase of E. coli is encoded by the gene tyrB. TyrB homologs and variants are known. For example, such homologs and variants include tyrB (Bordetella petrii) gi|163857093|ref|YP_(—)001631391.1|(163857093); tyrB (Bordetella petrii) gi|163260821|emb|CAP43123.1|(163260821); aminotransferase gi|551844|gb|AAA24704.1|(551844); aminotransferase (Bradyrhizobium sp. BTAi1) gi|146404387|gb|ABQ32893.1|(146404387); tyrosine aminotransferase TyrB (Salmonella enterica) gi|4775574|emb|CAB40973.2|(4775574); tyrosine aminotransferase (Salmonella typhimurium LT2) gi|16422806|gb|AAL23072.1|(16422806); and tyrosine aminotransferase gi|148085|gb|AAA24703.1|(148085), each sequence of which is incorporated herein by reference.

Pyruvate oxidase catalyzes the conversion of pyruvate to acetate and CO₂. In E. coli, pyruvate oxidase is encoded by poxB. PoxB and homologs and variants thereof include, for example, pyruvate oxidase; PoxB (Escherichia coli) gi|685128|gb|AAB31180.1∥bbm|348451|bbs|154716(685128); PoxB (Pseudomonas fluorescens) gi|32815820|gb|AAP88293.1|(32815820); poxB (Escherichia coli) gi|25269169|emb|CAD57486.1|(25269169); pyruvate dehydrogenase (Salmonella enterica subsp. enterica serovar Typhi) gi|16502101|emb|CAD05337.1|(16502101); pyruvate oxidase (Lactobacillus plantarum) gi|41691702|gb|AAS10156.1|(41691702); pyruvate dehydrogenase (Bradyrhizobium Japonicum) gi|20257167|gb|AAM12352.1|(20257167); pyruvate dehydrogenase (Yersinia pestis KIM) gi|22126698|ref|NP_(—)670121.1|(22126698); pyruvate dehydrogenase (cytochrome) (Yersinia pestis biovar Antigua str. B42003004) gi|166211240|ref|ZP_(—)02237275.1|(166211240); pyruvate dehydrogenase (cytochrome) (Yersinia pestis biovar Antigua str. B42003004) gi|166207011|gb|EDR51491.1|(166207011); pyruvate dehydrogenase (Pseudomonas syringae pv. tomato str. DC3000) gi|28869703|ref|NP 792322.1|(28869703); pyruvate dehydrogenase (Salmonella typhimurium LT2) gi|16764297|ref|NP_(—)459912.1|(16764297); pyruvate dehydrogenase (Salmonella enterica subsp. enterica serovar Typhi str. CT18) gi|16759808|ref|NP_(—)455425.1|(16759808); pyruvate dehydrogenase (cytochrome) (Coxiella burnetii Dugway 5J108-111) gi|154706110|ref|YP_(—)001424132.1|(154706110); pyruvate dehydrogenase (Clavibacter michiganensis subsp. michiganensis NCPPB 382) gi|148273312|ref|YP_(—)001222873.1|(148273312); pyruvate oxidase (Lactobacillus acidophilus NCFM) gi|58338213|ref|YP_(—)194798.1|(58338213); and pyruvate dehydrogenase (Yersinia pestis CO92) gi|16121638|ref|NP_(—)404951.1|(16121638), the sequences of each accession number are incorporated herein by reference.

L-threonine 3-dehydrogenase (EC 1.1.1.103) catalyzes the conversion of L-threonine to L-2-amino-3-oxobutanoate. The gene tdh encodes an L-threonine 3-dehydrogenase. There are approximately 700 L-threonine 3-dehydrogenases from bacterial organism recognized in NCBI. Various homologs and variants of tdh include, for example, L-threonine 3-dehydrogenase gi|135560|sp|P07913.1|TDH_ECOLI(135560); L-threonine 3-dehydrogenase gi|166227854|sp|A4TSC6.1|TDH_YERPP(166227854); L-threonine 3-dehydrogenase gi|166227853|sp|A1JHX8.1|TDH_YERE8(166227853); L-threonine 3-dehydrogenase gi|166227852|sp|A6UBM6.1|TDH_SINMW(166227852); L-threonine 3-dehydrogenase gi|166227851|sp|A1RE07.1|TDH_SHESW(166227851); L-threonine 3-dehydrogenase gi|166227850|sp|A0L2Q3.1|TDH_SHESA(166227850); L-threonine 3-dehydrogenase gi|166227849|sp|A4YCC5.1|TDH_SHEPC(166227849); L-threonine 3-dehydrogenase gi|166227848|sp|A3QJC8.1|TDH_SHELP(166227848); L-threonine 3-dehydrogenase gi|166227847|sp|A6WUG6.1|TDH_SHEB8(166227847); L-threonine 3-dehydrogenase gi|166227846|sp|A3CYN0.1|TDH_SHEB5(166227846); L-threonine 3-dehydrogenase gi|166227845|sp|A1S1Q3.1|TDH_SHEAM(166227845); L-threonine 3-dehydrogenase gi|166227844|sp|A4FND4.1|TDH_SACEN(166227844); L-threonine 3-dehydrogenase gi|166227843|sp|A1SVW5.1|TDH_PSYIN(166227843); L-threonine 3-dehydrogenase gi|166227842|sp|A51GK7.1|TDH_LEGPC(166227842); L-threonine 3-dehydrogenase gi|166227841|sp|A6TFL2.1|TDH_KLEP7(166227841); L-threonine 3-dehydrogenase gi|166227840|sp|A4IZ92.1|TDH_FRATW(166227840); L-threonine 3-dehydrogenase gi|166227839|sp|A0Q5K3.1|TDH_FRATN(166227839); L-threonine 3-dehydrogenase gi|166227838|sp|A7NDM9.1|TDH_FRATF(166227838); L-threonine 3-dehydrogenase gi|166227837|sp|A7MID0.1|TDH_ENTS8(166227837); and L-threonine 3-dehydrogenase gi|166227836|sp|A1AHF3.1|TDH_ECOK1(166227836), the sequences associated with each accession number are incorporated herein by reference.

Acetohydroxy acid synthases (e.g. ilvH) and acetolactate synthases (e.g., alsS, ilvB, ilvI) catalyze the synthesis of the branched-chain amino acids (valine, leucine, and isoleucine). IlvH encodes an acetohydroxy acid synthase in E. coli (see, e.g., acetohydroxy acid synthase AHAS III (IlvH) (Escherichia coli) gi|40846|emb|CAA38855.1|(40846), incorporated herein by reference). Homologs and variants as well as operons comprising ilvH are known and include, for example, ilvH (Microcystis aeruginosa PCC 7806)gi|159026908|emb|CAO89159.1|(159026908); IlvH (Bacillus amyloliquefaciens FZB42) gi|154686966|ref|YP_(—)001422127.1|(154686966); IlvH (Bacillus amyloliquefaciens FZB42) gi|154352817|gb|ABS74896.1|(154352817); IlvH (Xenorhabdus nematophila) gi|131054140|gb|AB032787.1|(131054140); IlvH (Salmonella typhimurium) gi|7631124|gb|AAF65177.1|AF117227_(—)2(7631124), ilvN (Listeria innocua) gi|16414606|emb|CAC97322.1|(16414606); ilvN (Listeria monocytogenes) gi|16411438|emb|CAD00063.1|(16411438); acetohydroxy acid synthase (Caulobacter crescentus) gi|408939|gb|AAA23048.1|(408939); acetohydroxy acid synthase I, small subunit (Salmonella enterica subsp. enterica serovar Typhi) gi|16504830|emb|CAD03199.1|(16504830); acetohydroxy acid synthase, small subunit (Tropheryma whipplei TW08/27) gi|28572714|ref|NP_(—)789494.1|(28572714); acetohydroxy acid synthase, small subunit (Tropheryma whipplei TW08/27) gi|28410846|emb|CAD67232.1|(28410846); acetohydroxy acid synthase I, small subunit (Salmonella enterica subsp. enterica serovar Paratyphi A str. ATCC 9150) gi|56129933|gb|AAV79439.1|(56129933); acetohydroxy acid synthase small subunit; acetohydroxy acid synthase, small subunit gi|551779|gb|AAA62430.1|(551779); acetohydroxy acid synthase I, small subunit (Salmonella enterica subsp. enterica serovar Typhi Ty2) gi|29139650|gb|AAO71216.1|(29139650); acetohydroxy acid synthase small subunit (Streptomyces cinnamonensis) gi|5733116|gb|AAD49432.1|AF175526_(—)1(5733116); acetohydroxy acid synthase large subunit; and acetohydroxy acid synthase, large subunit gi|400334|gb|AAA62429.1|(400334), the sequences associated with the accession numbers are incorporated herein by reference. Acetolactate synthase genes include alsS and ilvI. Homologs of ilvI and alsS are known and include, for example, acetolactate synthase small subunit (Bifidobacterium longum NCC2705) gi|23325489|gb|AAN24137.1|(23325489); acetolactate synthase small subunit (Geobacillus stearothermophilus) gi|19918933|gb|AAL99357.1|(19918933); acetolactate synthase (Azoarcus sp. BH72) gi|119671178|emb|CAL95091.1|(119671178); Acetolactate synthase small subunit (Corynebacterium diphtheriae) gi|38199954|emb|CAE49622.1|(38199954); acetolactate synthase (Azoarcus sp. BH72) gi|119669739|emb|CAL93652.1|(119669739); acetolactate synthase small subunit (Corynebacterium jeikeium K411) gi|68263981|emb|CAI37469.1|(68263981); acetolactate synthase small subunit (Bacillus subtilis) gi|1770067|emb|CAA99562.1|(1770067); Acetolactate synthase isozyme 1 small subunit (AHAS-I) (Acetohydroxy-acid synthase I small subunit) (ALS-I) gi|83309006|sp|P0ADF8.1|ILVN_ECOLI(83309006); acetolactate synthase large subunit (Geobacillus stearothermophilus) gi|19918932|gb|AAL99356.1|(19918932); and Acetolactate synthase, small subunit (Thermoanaerobacter tengcongensis MB4) gi|20806556|ref|NP_(—)621727.1|(20806556), the sequences associated with the accession numbers are incorporated herein by reference. There are approximately 1120 ilvB homologs and variants listed in NCBI.

Acetohydroxy acid isomeroreductase is the second enzyme in parallel pathways for the biosynthesis of isoleucine and valine. IlvC encodes an acetohydroxy acid isomeroreductase in E. coli. Homologs and variants of ilvC are known and include, for example, acetohydroxyacid reductoisomerase (Schizosaccharomyces pombe 972h−) gi|162312317|ref|NP_(—)001018845.2|(162312317); acetohydroxyacid reductoisomerase (Schizosaccharomyces pombe) gi|3116142|emb|CAA18891.1|(3116142); acetohydroxyacid reductoisomerase (Saccharomyces cerevisiae YJM789) gi|151940879|gb|EDN59261.1|(151940879); Ilv5p: acetohydroxyacid reductoisomerase (Saccharomyces cerevisiae) gi|609403|gb|AAB67753.1|(609403); ACL198Wp (Ashbya gossypii ATCC 10895) gi|45185490|ref|NP_(—)983206.1|(45185490); ACL198Wp (Ashbya gossypii ATCC 10895) gi|44981208|gb|AAS51030.1|(44981208); acetohydroxy-acid isomeroreductase; Ilv5x (Saccharomyces cerevisiae) gi|957238|gb|AAB33579.1∥bbm|369068|bbs|165406(957238); acetohydroxy-acid isomeroreductase; Ilv5g (Saccharomyces cerevisiae) gi|957236|gb|AAB33578.1∥bbm|369064|bbs|165405(957236); and ketol-acid reductoisomerase (Schizosaccharomyces pombe) gi|2696654|dbj|BAA24000.1|(2696654), each sequence associated with the accession number is incorporated herein by reference.

Dihydroxy-acid dehydratases catalyzes the fourth step in the biosynthesis of isoleucine and valine, the dehydratation of 2,3-dihydroxy-isovaleic acid into alpha-ketoisovaleric acid. IlvD and ilv3 encode a dihydroxy-acid dehydratase. Homologs and variants of dihydroxy-acid dehydratases are known and include, for example, IlvD (Mycobacterium leprae) gi|2104594|emb|CAB08798.1|(2104594); dihydroxy-acid dehydratase (Tropheryma whipplei TW08/27) gi|28410848|emb|CAD67234.1|(28410848); dihydroxy-acid dehydratase (Mycobacterium leprae) gi|13093837|emb|CAC32140.1|(13093837); dihydroxy-acid dehydratase (Rhodopirellula baltica SH 1) gi|32447871|emb|CAD77389.1|(32447871); and putative dihydroxy-acid dehydratase (Staphylococcus aureus subsp. aureus MRSA252) gi|49242408|emb|CAG41121.1|(49242408), each sequence associated with the accession numbers are incorporated herein by reference.

2-ketoacid decarboxylases catalyze the conversion of a 2-ketoacid to the respective aldehyde. For example, 2-ketoisovalerate decarboxylase catalyzes the conversion of 2-ketoisovalerate to isobutyraldehyde. A number of 2-ketoacid decarboxylases are known and are exemplified by the pdc, pdcl, pdc5, pdc6, arol0, thI3, kdcA and kivd genes. Exemplary homologs and variants useful for the conversion of a 2-ketoacid to the respective aldehyde comprise sequences designated by the following accession numbers and identified enzymatic activity: gi|44921617|gb|AAS49166.1| branched chain alpha-keto acid decarboxylase (Lactococcus lactis); gi|15004729|ref|NP_(—)149189.1| Pyruvate decarboxylase (Clostridium acetobutylicum ATCC 824); gi|82749898|ref|YP_(—)415639.1| probable pyruvate decarboxylase (Staphylococcus aureus RF122); gi|77961217|ref|ZP_(—)00825060.1| COG3961: Pyruvate decarboxylase and related thiamine pyrophosphate-requiring enzymes (Yersinia mollaretii ATCC 43969); gi|71065418|ref|YP_(—)264145.1| putative pyruvate decarboxylase (Psychrobacter arcticus 273-4); gi|16761331|ref|NP_(—)456948.1| putative decarboxylase (Salmonella enterica subsp. enterica serovar Typhi str. CT18); gi|93005792|ref|YP_(—)580229.1| Pyruvate decarboxylase (Psychrobacter cryohalolentis K5); gi|23129016|ref|ZP_(—)00110850.1| CO1TG3961: Pyruvate decarboxylase and related thiamine pyrophosphate-requiring enzymes (Nostoc punctiforme PCC 73102); gi|16417060|gb|AAL|8557.1|AF354297_(—)1 pyruvate decarboxylase (Sarcina ventriculi); gi|15607993|ref|NP_(—)215368.1|PROBABLE PYRUVATE OR INDOLE-3-PYRUVATE DECARBOXYLASE PDC (Mycobacterium tuberculosis H37Rv); gi|41406881|ref|NP_(—)959717.1| Pdc (Mycobacterium avium subsp. paratuberculosis K-10); gi|91779968|ref|YP_(—)555176.1| putative pyruvate decarboxylase (Burkholderia xenovorans LB400); gi|15828161|ref|NP_(—)302424.1| pyruvate (or indolepyruvate) decarboxylase (Mycobacterium leprae TN); gi|118616174|ref|YP_(—)904506.1| pyruvate or indole-3-pyruvate decarboxylase Pdc (Mycobacterium ulcerans Agy99); gi|67989660|ref|NP_(—)001018185.1| hypothetical protein SPAC3H8.01 (Schizosaccharomyces pombe 972h−); gi|21666011|gb|AAM73540.1|AF282847_(—)1 pyruvate decarboxylase PdcB (Rhizopus oryzae); gi|69291130|ref|ZP_(—)00619161.1| Pyruvate decarboxylase:Pyruvate decarboxylase (Kineococcus radiotolerans SRS30216); gi|66363022|ref|XP_(—)628477.1| pyruvate decarboxylase (Cryptosporidium parvum Iowa 11); gi|70981398|ref|XP_(—)731481.1| pyruvate decarboxylase (Aspergillus fumigatus Af 293); gi|121704274|ref|XP_(—)001270401.1| pyruvate decarboxylase, putative (Aspergillus clavatus NRRL 1); gi|119467089|ref|XP_(—)001257351.1| pyruvate decarboxylase, putative (Neosartorya fischeri NRRL 181); gi|26554143|ref|NP_(—)758077.1| pyruvate decarboxylase (Mycoplasma penetrans HF-2); gi|21666009|gb|AAM73539.1|AF282846_(—)1 pyruvate decarboxylase PdcA (Rhizopus oryzae).

Alcohol dehydrogenases (adh) catalyze the final step of amino acid catabolism, conversion of an aldehyde to a long chain or complex alcohol. Various adh genes are known in the art. As indicated herein adh1 homologs and variants include, for example, adh2, adh3, adh4, adh5, adh 6 and sfal (see, e.g., SFA (Saccharomyces cerevisiae) gi|288591|emb|CAA48161.1|(288591); the sequence associated with the accession number is incorporated herein by reference).

Citramalate synthase catalyzes the condensation of pyruvate and acetate. CimA encodes a citramalate synthase. Homologs and variants are known and include, for example, citramalate synthase (Leptospira biflexa serovar Patoc) gi|116664687|gb|ABK13757.1|(116664687); citramalate synthase (Leptospira biflexa serovar Monteralerio) gi|116664685|gb|ABK13756.1|(116664685); citramalate synthase (Leptospira interrogans serovar Hebdomadis) gi|116664683|gb|ABK13755.1|(116664683); citramalate synthase (Leptospira interrogans serovar Pomona) gi|116664681|gb|ABK13754.1|(116664681); citramalate synthase (Leptospira interrogans serovar Australis) gi|116664679|gb|ABK13753.1|(116664679); citramalate synthase (Leptospira interrogans serovar Autumnalis) gi|116664677|gb|ABK13752.1|(116664677); citramalate synthase (Leptospira interrogans serovar Pyrogenes) gi|116664675|gb|ABK13751.1|(116664675); citramalate synthase (Leptospira interrogans serovar Canicola) gi|116664673|gb|ABK13750.1|(116664673); citramalate synthase (Leptospira interrogans serovar Lai) gi|116664671|gb|ABK13749.1|(116664671); CimA (Leptospira meyeri serovar Semaranga) gi|119720987|gb|ABL98031.1|(119720987); (R)-citramalate synthase gi|2492795|sp|Q58787.1|CIMA_METJA(2492795); (R)-citramalate synthase gi|22095547|sp|P58966.1|CIMA_METMA(22095547); (R)-citramalate synthase gi|22001554|sp|Q8TJJ1.1|CIMA_METAC(22001554); (R)-citramalate synthase gi|22001553|sp1026819.1|CIMA_METTH(22001553); (R)-citramalate synthase gi|22001555|sp|Q8TYB1.1|CIMA_METKA(22001555); (R)-citramalate synthase (Methanococcus maripaludis S2) gi|45358581|ref|NP_(—)988138.1|(45358581); (R)-citramalate synthase (Methanococcus maripaludis S2) gi|44921339|emb|CAF30574.1|(44921339); and similar to (R)-citramalate synthase (Candidatus Kuenenia stuttgartiensis) gi|91203541|emb|CAJ71194.1|(91203541), each sequence associated with the foregoing accession numbers is incorporated herein by reference.

EXAMPLES

A cyanobacterium, S. elongatus, was engineered as follows. The ketoacid decarboxylase gene kivd from Lactococcus lactis was expressed using an expression cassette under the control of the isopropyl-β-D-thiogalactoside (IPTG) inducible promoter Ptrc (FIG. 1C). This DNA fragment was integrated into neutral site I (NSI)14 by homologous recombination, resulting in SA578 (FIG. 1D). To increase the flux to the keto acid precursor, 2-ketoisovalerate (KIV), the alsS gene from Bacillus subtilis and the ilvC and ilvD genes from Escherichia coli were inserted into neutral site II (NSII) of the SA578 genome, resulting in SA590. (FIG. 1E). All three enzyme assays of SA590 lysates demonstrated higher activity than those from SA578 (FIG. 1F), indicating that alsS (B. subtilis), ilvC (E. coli) and ilvD (E. coli) are expressed and functional in S. elongatus. Because the vapor pressure of isobutyraldehyde is relatively high, it can be removed readily from the culture medium during production by the bubbling of air. Evaporated isobutyraldehyde was then condensed with a Graham condenser.

The strain was cultured in a Roux culture bottle at 30° C. Isobutyraldehyde concentrations in the culture medium and the trap were measured. The trap was refreshed daily. The strain produced 723 mg/l isobutyraldehyde in 12 d with an average production rate of 2,500 μg l⁻¹h⁻¹ (FIG. 1G-H). This number is very encouraging, as it is already close to the benchmark. The isobutyraldehyde production rate remained constant for the first 9 d, but the production rate decreased after the tenth day (FIG. 1H-I). When the culture was resuspended in fresh medium after 10 d, the bacteria regained their productivity (˜60 mg l⁻¹ d⁻¹), suggesting that some inhibitory metabolites accumulated during the cultivation. As expected, during the production process the isobutyraldehyde concentration in the culture medium remained low, around 20 mg/l (FIG. 1I). This low concentration would reduce toxicity to cells and prolong the production phase. This strain did not produce isobutanol, indicating that endogenous alcohol dehydrogenase (ADH) activity toward isobutyraldehyde was not detectable.

Isobutyraldehyde can also be converted to isobutanol by cyanobacteria. Increasing attention has been paid to isobutanol as a potential substitute for gasoline or as a chemical feedstock. Thus, it would be worthwhile demonstrating the biological feasibility of isobutanol production by cyanobacteria. To demonstrate the direct synthesis of isobutanol, three alcohol dehydrogenases (ADH2 from Saccharomyces cerevisiae, YqhD from E. coli, and AdhA from L. lactis) along with Kivd from L. lactis were used. Their corresponding genes were integrated downstream of kivd (FIG. 1D) individually, resulting in strains SA413, SA561 and SA562. After KIV was added to the growth medium the reaction products isobutyraldehyde and isobutanol were detected (FIG. 1K). Among the three dehydrogenases tested, YqhD was the most active in S. elongatus (FIG. 1K). YqhD is an NADPH-dependent enzyme, whereas AdhA and ADH2 are NADH-dependent. These results suggest that the NADH generated in the cell was insufficient for the NADH-dependent ADH. To increase the flux to KIV, the amplified KIV pathway (FIG. 1E) was combined with the alcohol-producing pathway (Kind and YqhD). The strain (SA579) produced 450 mg/l of isobutanol in 6 d (FIG. 1M-O and FIG. 1L).

The tolerance of S. elongatus to isobutyraldehyde and isobutanol was also measured (FIG. 1P). Wild-type S. elongatus was able to tolerate concentrations of isobutyraldehyde up to 750 mg/l (FIG. 1Q), but showed growth retardation in the presence of the same concentration of isobutanol. This result shows that isobutyraldehyde is less toxic to the cell than isobutanol. In addition, the isobutyraldehyde tolerance level of S. elongatus is much higher than the concentration found in the culture medium during production. These data are consistent with the result that the isobutyraldehyde production strain produced constantly for 9 d in this system. Thus, the in situ product removal system effectively avoids toxicity effects.

Although productivity (total product divided by volume and time) is not the only factor that determines the potential of a production system, the productivities of the engineered cyanobacteria for isobutyraldehyde and isobutanol demonstrated here are already higher than the productivites of cyanobacteria demonstrated for hydrogen or ethanol (FIG. 10). As producing biodiesel from microalgae has been proposed as one of the most efficient methods, the algal diesel productivity (1×10⁵ liter ha⁻¹ per year, which corresponds to about 4,000 μl l⁻¹ h⁻¹ assuming 1 m characteristic dimension) was used as a benchmark for isobutyraldehyde production. Although the productivity of lab-scale experiments cannot be directly translated to industrial-scale production, our productivity of isobutyraldehyde (6,230 μg l⁻¹ h⁻¹) is encouraging (FIG. 10). This result demonstrates the technical feasibility for direct conversion of CO₂ to fuels or chemicals, which could become an economically feasible option after further improvement. The strategy further expands the utility of photosynthesis and bypasses the need for biomass deconstruction and may therefore provide an alternative path for addressing two of humanity's most pressing problems: energy and climate change.

Reagents.

Restriction enzymes and Antarctic phosphatase were from New England Biolabs. Rapid DNA ligation kit was from Roche. KOD DNA polymerase was from EMD Chemicals. Oligonucleotides were from Eurofins MWG Operon. The chemicals, ribulose-1,5-bisphosphate, ribulose-1,5-bisphosphate carboxylase, NADPH, 2,4-dinitrophenylhydrazine, propionic acid, acetoin, 2-keto-isovalerate and cocarboxylase were obtained from Sigma-Aldrich. NaH₁₄CO₃ (specific activity 5 mCi/mmol) was purchased from American Radiolabeled Chemicals.

Strains and Plasmids Construction.

Strains and plasmids used in this work are described in the following table. The primers used are listed in the table below.

Table of strains and plasmids used in this study Strain Relevant genotype Synechococcus strains PCC7942 wild-type SA413 kivd-ADH2 integrated at NSI in PCC7942 chromosome SA561 kivd-yqhD integrated at NSI in PCC7942 chromosome SA562 kivd-adhA integrated at NSI in PCC7942 chromosome SA578 kivd integrated at NSI in PCC7942 chromosome SA579 alsS-ilvC-ilvD integrated at NSII in SA561 chromosome SA590 alsS-ilvC-ilvD integrated at NSII in SA578 chromosome Plasmids pAM2991 NSI targeting vector; Ptrc pMMB66EH IncQ; AmpR; Ptac pSA55 Co1E1 ori; AmpR; PL1acO1: kivd-ADH2 pSA65 Co1E1 ori; AmpR; PL1acO1: kivd-adhA pSA68 Co1E1 ori; AmpR; PL1acO1: alsS-ilvC-ilvD pSA78 From pAM2991 with kivd-ADH2 pSA126 NSII targeting vector; carries PL1acO1::alsS-ilvC-ilvD pSA129 Co1E1 ori; AmpR; PL1acO1: kivd pSA138 Co1E1 ori; AmpR; PL1acO1: kivd-yqhD pSA149 From pAM2991 with kivd-adhA pSA150 From pAM2991 with kivd-yqhD pSA155 From pAM2991 with kivd

Table of synthetic oligonucleotides used in this study name sequence (SEQ ID NO:) A148 GCCACCGGTCTCCAATTCTATACAGTAGGAGATTACCTATTAG (1) A149 CGGGATCCTTATTTAGAAGTGTCAACAACGTAT(2) A217 GGCGAGCTCCGATCGCTTTGGGACTTGGAACGGT(3) A218 GGCGAGCTCAAATCACCAGCTGAAACGGTGAAGT(4) A219 CGCCTAGGAACCGTTCCTGCGCGATCGCTCTTA(5) A220 CGCCTAGGTAAGCGGGCCACGGCAGCGAAAGGG(6) A258 CGGGATCCTTATTTAGTAAAATCAATGACCATT(7) A259 CGGGATCCTTAGCGGGCGGCTTCGTATATACGG(8) A262 CGGGATCCTTATGATTTATTTTGTTCAGCAAAT(9) A308 GAGTGGCAATTGATGCCCAAGACGCAATCTGCCGCAG(10) A309 GGTATATCTCCTTCTTTTAGAGCTTGTCCATCGTTTCGAAT (11) A310 AACGATGGACAAGCTCTAAAAGAAGGAGATATACCATGAAAAC TCTGCCCAAAGAGCGTC(12) A311 CGGGATCCTTAGTAGCGGCCGGGACGATGAACG(13) A315 GGAAGATCTTTCGTGTCGCTCAAGGCGCACTCCC(14) A316 GGAAGATCTGTCTTGCCACGCCGAGCACCTGGTC(15) A317 CGGGATCCGATATCTGGCGAAAATGAGACGTTG(16) A318 GGGCCTGCAGGATATCAAATTACGCCCCGCCCTGC(17)

The Neutral Site I (NSI) Targeting Vector.

Strains that express kivd and adh were constructed by insertion of an expression cassette into NSI14. The genes kivd and adh were cloned into the NSI targeting vector, pAM2991, under the IPTG-inducible Ptrc promoter. The coding region of kivd-ADH2, kivd-adhA, kivd-yqhD and kivd were amplified from pSA55, pSA65, pSA134 and pSA129, respectively, using oligonucleotides A148 and A149, A148-A258, A148-A259 and A148-A262, respectively. The resulting plasmids were named pSA78 (kivd-ADH2), pSA149 (kivd-adhA), and pSA150 (kivd-yqhD) and pSA155 (kivd).

The Neutral Site II (NSII)17 Targeting Vector.

Construction of pSA68, which contains alsS (B. subtilis)-ilvC-ilvD (E. coli), was constructed as previously described. To clone the 5′ fragment of NSII, genomic DNA of S. elongatus was used as the PCR template with primers A217 and A218. PCR products were digested with SacI and cloned into pSA68 cut with the same enzyme, creating pSA117. A correct orientation of the fragment was confirmed by PCR. To clone the chloramphenicol resistance gene, pACYC184 was used as the PCR template with primers A225 and A226. PCR products were digested with SpeI and cloned into pSA117 cut with the same enzyme, creating pSA122. A correct orientation of the fragment was confirmed by PCR. To clone the 3′ fragment of NSII, genomic DNA of S. elongatus was used as the PCR template with primers A219 and A220. PCR products were digested with AvrII and cloned into pSA122 cut with the same enzyme, creating pSA126. A correct orientation of the fragment was confirmed by PCR.

Transformation of S. elongatus.

Transformation of S. elongatus was carried out as described. Cyanobacterial transformants with the targeting vectors were selected on BG-11 agar plates supplemented with antibiotics as appropriate; 20 μg/ml spectinomycin, 10 μg/ml kanamycin and 5 μg/ml chloramphenicol. Results of the transformation were confirmed by PCR and enzyme assays.

Medium and Culture Conditions.

Wild-type S. elongatus and mutant strains were grown in a modified BG-11 medium with the following modifications: 50 mM NaHCO₃ and 10 mg/l thiamine were added. For an experiment with 5% CO₂ bubbling, 50 mM NaHCO₃ was not added. Cyanobacterial cells were grown at 30° C. under fluorescent light (55 μE s⁻¹ m⁻²), which was provided by eight 86-cm 20-W fluorescent tubes placed 15 cm from the cell culture. Cell growth was monitored by measuring OD730 of each culture.

Culture Conditions for Isobutanol and Isobutyraldehyde Production.

For isobutyraldehyde and isobutanol production, cells were grown in 600 ml medium in 1,000-ml Roux culture bottles that were aerated by air or air containing 5% CO₂. The culture was allowed to grow at 30° C. to OD₇₃₀ of 0.4-0.6, at which point 1 mM IPTG was added. Daily, one-tenth the total volume of cell culture was removed from the cell culture. Then the same volume of fresh medium containing 0.5 M NaHCO₃ was added to cell culture. pH of cell culture with NaHCO₃ was adjusted to 7.5 with 10 N HCl everyday. Utilization of 5% CO₂ stabilized the pH of cell culture around ˜7.0, thus the pH was not adjusted. Presumably, the constant pH is due to the balance between CO₂ dissolution and consumption.

Quantification of the Products.

The alcohol and aldehyde compounds produced were quantified by a gas chromatograph equipped with a flame ionization detector. Other secreted metabolites were quantified by a high-performance liquid chromatography.

Preparation of Cell-Free Extracts.

Cells were collected 24 h after induction by centrifugation (4,000 g, 10 min, 25° C.). For the Als, IlvC and IlvD assays, the cells were washed once in 1 mM MgCl₂ and 100 mM 3-(N-morpholino) propanesulfonic acid (MOPS), pH 7.0, then resuspended in the same buffer. The cells were broken by passage through a chilled French pressure cell at 20,000 p.s.i. (4° C.) for a total of three times. Total protein measurements were made with the Bradford protein assay kit from Bio-Rad.

Als Assay.

The Als assay was performed as described previously, with the exception that the reaction mixture contained 20 mM sodium pyruvate, 100 mM MOPS buffer, pH 7.0, 1 mM MgCl₂ and 100 μM cocarboxylase. The concentration of acetoin produced was determined by a standard curve created using pure acetoin. One specific unit of Als activity corresponds to the formation of 1 nmol of acetoin per mg of soluble protein per min at 37° C.

IlvC Assay.

To measure the reduction of 2-acetolactate to 2,3-dihydroxy-isovalerate, the oxidation of NADPH was monitored by a decrease in absorbance at 340 nm. The substrate, 2-acetolactate, was first produced in a separate reaction as described for the Als assay using purified, heterogeneously expressed B. subtilis AlsS in E. coli strain BL21. From this reaction 180 μl was added to 200 mM potassium phosphate buffer, pH 7.5, 4 mM MgCl₂ and 0.1 mM NADPH for a final reaction volume of 1 ml. The samples were incubated at 30° C. for 5 min, then the reaction was initiated with the addition of cell extracts. Absorbance was measured at 340 nm. INC activity is expressed as nmol of NADPH oxidized per min per mg of soluble protein at 30° C.

IlvD Assay.

The IlvD assay was performed as described previously. The 500 μl reaction mixture contained 5 mM MgSO₄, 50 mM Tris-C1, pH 8.0, cell-free extract and 10 mM 2,3-dihydroxy-isovalerate. The substrate, 2,3-dihydroxy-isovalerate, was synthesized as described previously. After the reaction mixture was preincubated for 5 min at 37° C., the substrate was added to initiate the reaction. The samples were incubated for 15 min at 37° C. The reaction was terminated by the addition of 125 μl of 10% trichloroacetic acid, then 250 μl of saturated 2,4-dinitrophenylhydrazine in 2 N HCl was added to the samples. After 20 min at 25° C., 875 μl of 2.5 N NaOH was added and then the samples were incubated for another 30 min at 25° C. The samples were then spun down for 1 min to remove coagulated protein. Sample absorbances were measured at 550 nm. Standard curves were created from known amounts of KIV. The specific activity was calculated as 1 nmol of KIV synthesized per mg of soluble protein per min at 37° C.

O2 Production Measurements.

The S. elongatus cultures were similarly cultured and induced as they were for isobutyraldehyde production. Periodically, 2 ml culture samples were measured for OD₇₃₀ and O₂ production using the Oxygraph System (Hansatech Instruments). Data points represent triplicate measurements.

Attached hereto and incorporated herein, in addition to the figures, are sequences that are relevant to the practice of the disclosure. The sequences correspond to particular coding sequences and polypeptide sequence for enzymes useful in generating a biofuel. One of skill in the art can readily determine which sequence is appropriate for a referenced gene or homolog. For example, reference to kind, would include the sequence set forth in SEQ ID NO:18 (cDNA) and SEQ ID NO:19 (polypeptide), variants comprising a percent identity and having a decarboxylase function and homologs from other organisms.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims. 

What is claimed is:
 1. A recombinant Synechococcus elongatus microorganism that does not have endogenous alcohol dehydrogenase activity toward isobutyraldehyde and produces isobutyraldehyde, wherein the recombinant Synechococcus elongatus expresses an isobutyraldehyde producing metabolic pathway comprising the following enzymes and substrate to product conversions: an acetolactate synthase comprising an amino acid sequence with at least 85% identity SEQ ID NO:73 to catalyze the conversion of pyruvate to acetolactate, an acetohydroxy acid isomeroreductase comprising an amino acid sequence with at least 85% identity SEQ ID NO:35 to catalyze the conversion of acetolactate to 2,3-dihydroxy-isovalerate, a dihydroxyacid dehydratase comprising an amino acid sequence with at least 85% identity SEQ ID NO:37 to catalyze the conversion of 2,3-dihydroxy-isovalerate to 2-ketoisovalerate, and a 2-ketoisovalerate decarboxylase obtained from Lactococcus lactis comprising an amino acid sequence with at least 85% identity SEQ ID NO:19 to catalyze the conversion of 2-ketoisovalerate to isobutyraldehyde, and wherein one or more of the enzymes in the metabolic pathway is exogenous.
 2. The recombinant microorganism of claim 1, wherein the acetolactate synthase is exogenous, catalyzes the conversion of pyruvate to acetolactate and is obtained from Bacillus subtilis.
 3. The recombinant microorganism of claim 1, wherein the acetohydroxy acid isomeroreductase is exogenous, catalyzes the conversion of acetolactate to 2,3-dihydroxy-isovalerate and is obtained from Escherichia coli.
 4. The recombinant microorganism of claim 1, wherein the dihydroxyacid dehydratase is exogenous, catalyzes the conversion of 2,3-dihydroxy-isovalerate to 2-ketoisovalerate and is obtained from Escherichia coli.
 5. A method of preparing a recombinant Synechococcus elongatus microorganism that does not have endogenous alcohol dehydrogenase activity toward isobutyraldehyde and produces isobutyraldehyde comprising: transforming a Synechococcus elongatus microorganism with one or more targeting vectors comprising one or more polynucleotides encoding (i) one or more of an acetolactate synthase comprising an amino acid sequence with at least 85% identity SEQ ID NO:73 to catalyze the conversion of pyruvate to acetolactate, an acetohydroxy acid isomeroreductase comprising an amino acid sequence with at least 85% identity SEQ ID NO:35 to catalyze the conversion of acetolactate to 2,3-dihydroxy-isovalerate, a dihydroxyacid dehydratase comprising an amino acid sequence with at least 85% identity SEQ ID NO:37 to catalyze the conversion of 2,3-dihydroxy-isovalerate to 2-ketoisovalerate, and a 2-ketoisovalerate decarboxylase obtained from Lactococcus lactis comprising an amino acid sequence with at least 85% identity SEQ ID NO:19 to catalyze the conversion of 2-ketoisovalerate to isobutyraldehyde; and (ii) at least one inducible promoter, to prepare a recombinant Synechococcus elongatus microorganism, wherein the recombinant Synechococcus elongatus microorganism produces isobutyraldehyde.
 6. The recombinant microorganism of claim 2, wherein the acetolactate synthase obtained from Bacillus subtilis is SEQ ID NO:73.
 7. The recombinant microorganism of claim 3, wherein the acetohydroxyacid isomeroreductase obtained from Escherichia coli is SEQ ID NO.: 35 SEQ ID NO:35.
 8. The recombinant microorganism of claim 4, wherein the dihydroxyacid dehydratase obtained from Escherichia coli is SEQ ID NO:37.
 9. The recombinant microorganism of claim 1, wherein the 2-ketoisovalerate decarboxylate obtained from Lactococcus lactis is SEQ ID NO:19.
 10. A method of producing isobutyraldehyde comprising: (a) providing the recombinant Synechococcus elongatus microorganism of claim 1 in a culture medium; (b) culturing the recombinant microorganism of (a) in the presence of CO₂, wherein isobutyraldehyde is produced via photosynthesis and the metabolic pathway of the recombinant Synechococcus elongatus of (a); and (c) removing the isobutyraldehyde from the culture medium.
 11. The method of claim 10, wherein the acetolactate synthase obtained from Bacillus subtilis.
 12. The method of claim 10, wherein the acetohydroxy acid isomeroreductase is obtained from Escherichia coli.
 13. The method of claim 10, wherein the dihydroxy dehydratase is obtained from Escherichia coli.
 14. The method of claim 10, wherein the isobutyraldehyde is removed from the culture medium by gas bubbling.
 15. The method of claim 10, wherein the isobutyraldehyde is removed from the culture medium by evaporation.
 16. The method of claim 15, further comprising condensing the evaporated isobutyraldehyde.
 17. The method of claim 10, wherein isobutanol is not produced by the recombinant microorganism at a detectable level. 